Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Demography of the ecosystem engineer Crassostrea gigas, related to vertical freef accretion and reef persistence
    Walles, B. ; Mann, R.M. ; Ysebaert, T. ; Troost, K. ; Herman, P.M.J. ; Smaal, A.C. - \ 2015
    Estuarine Coastal and Shelf Science 154 (2015). - ISSN 0272-7714 - p. 224 - 233.
    sea-level rise - introduced pacific oysters - wadden sea - chesapeake bay - population-dynamics - shell dissolution - eastern oyster - james river - virginica - habitats
    Marine species characterized as structure building, autogenic ecosystem engineers are recognized worldwide as potential tools for coastal adaptation efforts in the face of sea level rise. Successful employment of ecosystem engineers in coastal protection largely depends on long-term persistence of their structure, which is in turn dependent on the population dynamics of the individual species. Oysters, such as-the Pacific oyster (Crassostrea gigas), are recognized as ecosystem engineers with potential for use in coastal protection. Persistence of oyster reefs is strongly determined by recruitment and shell production (growth), processes facilitated by gregarious settlement on extant shell substrate. Although the Pacific oyster has been introduced world-wide, and has formed dense reefs in the receiving coastal waters, the population biology of live oysters and the quantitative mechanisms maintaining these reefs has rarely been studied, hence the aim of the present work. This study had two objectives: (1) to describe the demographics of extant C. gigas reefs, and (2) to estimate vertical reef accretion rates and carbonate production in these oyster reefs. Three long-living oyster reefs (>30 years old), which have not been exploited since their first occurrence, were examined in the Oosterschelde estuary in the Netherlands. A positive reef accretion rate (7.0-16.9 mm year(-1) shell material) was observed, consistent with self-maintenance and persistent structure. We provide a framework to predict reef accretion and population persistence under varying recruitment, growth and mortality scenarios. (C) 2015 Elsevier Ltd. All rights reserved.
    Spatial heterogeneity of plant–soil feedback affects root interactions and interspecific competition
    Hendriks, M. ; Ravenek, J. ; Smit-Tiekstra, A.E. ; Paauw, J.W.M. van der; Caluwe, H. de; Putten, W.H. van der; Kroon, H. de; Mommer, L. - \ 2015
    New Phytologist 207 (2015)3. - ISSN 0028-646X - p. 830 - 840.
    nutrient heterogeneity - species-diversity - population-dynamics - relative abundance - deciduous woodland - temporal variation - borne pathogens - grassland - community - coexistence
    Plant-soil feedback is receiving increasing interest as a factor influencing plant competition and species coexistence in grasslands. However, we do not know how spatial distribution of plant-soil feedback affects plant below-ground interactions. We investigated the way in which spatial heterogeneity of soil biota affects competitive interactions in grassland plant species. We performed a pairwise competition experiment combined with heterogeneous distribution of soil biota using four grassland plant species and their soil biota. Patches were applied as quadrants of 'own' and 'foreign' soils from all plant species in all pairwise combinations. To evaluate interspecific root responses, species-specific root biomass was quantified using real-time PCR. All plant species suffered negative soil feedback, but strength was species-specific, reflected by a decrease in root growth in own compared with foreign soil. Reduction in root growth in own patches by the superior plant competitor provided opportunities for inferior competitors to increase root biomass in these patches. These patterns did not cascade into above-ground effects during our experiment. We show that root distributions can be determined by spatial heterogeneity of soil biota, affecting plant below-ground competitive interactions. Thus, spatial heterogeneity of soil biota may contribute to plant species coexistence in species-rich grasslands.
    Mobile dune fixation by a fast-growing clonal plant: a full life-cycle analysis
    Werger, M.J.A. ; During, H.J. ; Zuidema, P.A. - \ 2015
    Scientific Reports 5 (2015). - ISSN 2045-2322 - 7 p.
    integral projection models - inner mongolian dune - comparative demography - population-dynamics - psammochloa-villosa - relative importance - hedysarum-laeve - desert cactus - china - growth
    Desertification is a global environmental problem, and arid dunes with sparse vegetation are especially vulnerable to desertification. One way to combat desertification is to increase vegetation cover by planting plant species that can realize fast population expansion, even in harsh environments. To evaluate the success of planted species and provide guidance for selecting proper species to stabilize active dunes, demographic studies in natural habitats are essential. We studied the life history traits and population dynamics of a dominant clonal shrub Hedysarum laeve in Inner-Mongolia, northern China. Vital rates of 19057 ramets were recorded during three annual censuses (2007–2009) and used to parameterize Integral Projection Models to analyse population dynamics. The life history of H. laeve was characterized by high ramet turnover and population recruitment entirely depended on clonal propagation. Stochastic population growth rate was 1.32, suggesting that the populations were experiencing rapid expansion. Elasticity analysis revealed that clonal propagation was the key contributor to population growth. The capacity of high clonal propagation and rapid population expansion in mobile dunes makes H. laeve a suitable species to combat desertification. Species with similar life-history traits to H. laeve are likely to offer good opportunities for stabilizing active dunes in arid inland ecosystems.
    Growth of anaerobic methane oxidizing archaea and sulfate reducing bacteria in a high pressure membrane-capsule bioreactor
    Timmers, P.H.A. ; Gieteling, J. ; Widjaja-Greefkes, H.C.A. ; Plugge, C.M. ; Stams, A.J.M. ; Lens, P.N.L. ; Meulepas, R.J.W. - \ 2015
    Applied and Environmental Microbiology 81 (2015)4. - ISSN 0099-2240 - p. 1286 - 1296.
    cold-seep sediments - 16s ribosomal-rna - gradient gel-electrophoresis - guaymas basin - hydrothermal sediments - microbial diversity - marine-sediments - population-dynamics - community structure - gene database
    Anaerobic methane oxidizing communities of archaea (ANME) and sulfate reducing bacteria (SRB) grow slowly, which limits physiological studies. High methane partial pressure was previously successfully applied to stimulate growth, but it is not clear how different ANME subtypes and associated sulfate reducing bacteria (SRB) are affected by it. Here, we report growth of ANME/SRB in a membrane-capsule bioreactor inoculated with Eckernförde Bay sediment that combines high pressure incubation (10.1 MPa methane) and thorough mixing (100 rpm) with complete cell retention by a 0.2 µm membrane. Results were compared to previously obtained data from an ambient-pressure (0.101 MPa methane) bioreactor inoculated with the same sediment. Labelled-methane oxidation rates were not higher at 10.1 MPa, likely because measurements were done at ambient pressure. The subtype ANME-2a/b was abundant in both reactors, but subtype ANME-2c was only enriched at 10.1 MPa. SRB at 10.1 MPa mainly belonged to the SEEP-SRB2, Eel-1 group and Desulforomonadales and not to the typically found SEEP-SRB1. Increase of ANME-2a/b occurred in parallel with increase of SEEP-SRB2 which was previously only found associated with ANME-2c. Our results imply that the syntrophic association is flexible and that methane pressure and sulfide concentration influence growth of different ANME-SRB consortia. We also studied the effect of elevated methane pressure on methane production and oxidation by a mixture of methanogenic and sulfate-reducing sludge. Here, methane oxidation rates decreased and were not coupled to sulfide production, indicating trace methane oxidation during net methanogenesis and not anaerobic methane oxidation, even at high methane partial pressure.
    Fish abundance, fisheries, fish trade and consumption in sixteenth-century Netherlands as described by Adriaen Coenen
    Bennema, F.P. ; Rijnsdorp, A.D. - \ 2015
    Fisheries Research 161 (2015). - ISSN 0165-7836 - p. 384 - 399.
    pleuronectes-platessa l - atlantic bluefin tuna - southern north-sea - cod gadus-morhua - wadden sea - population-dynamics - medieval europe - resource use - lower rhine - history
    Concern about fisheries impact on marine ecosystems has raised the interest in the reconstruction of the state of marine ecosystems and the nature of the human activities in the past. We present late 16th century information on the occurrence and relative abundance of biota in Dutch coastal and inland waters (50 marine fish, 13 diadromous or freshwater and 4 marine mammal species), as well as a description of the sea fisheries (target species, fishing grounds, gear), fish trade, export, and fish consumption in Holland as documented in the handwritten Fish Book by Adriaen Coenen (1577–1581). The species composition and abundances are compared to published trawl survey data from around 1900 and in the 1990s. Fish species that have disappeared almost completely, were already rare around 1900 and are characterised by a large body size (rays and sharks, sturgeon, ling), whereas currently abundant species were already abundant in the 16th century. Intensive fisheries for herring occurred near Orkney, Fairhill and Shetland. Coastal and freshwater fisheries provided fresh fish for local as well as export markets, but also provided bait for the massive offshore hook and line fishery for the production of salted cod, which remained largely unnoticed. Dried flatfish were exported to Germany. Consumption of fish and marine invertebrates differed between social classes. Coenen distinguished eight consumer categories, a refinement of the categories ‘rich’ and ‘poor’ used in archaeological studies.
    No evidence of the effect of extreme weather events on annual occurrence of four groups of ectothermic species
    Malinowska, A.H. ; Strien, A.J. van; Verboom, J. ; Wallis de Vries, M.F. ; Opdam, P. - \ 2014
    PLoS ONE 9 (2014)10. - ISSN 1932-6203 - 10 p.
    climate-change - metapopulation dynamics - habitat fragmentation - population-dynamics - occupancy models - european climate - range expansion - dispersal - trends - impact
    Weather extremes may have strong effects on biodiversity, as known from theoretical and modelling studies. Predicted negative effects of increased weather variation are found only for a few species, mostly plants and birds in empirical studies. Therefore, we investigated correlations between weather variability and patterns in occupancy, local colonisations and local extinctions (metapopulation metrics) across four groups of ectotherms: Odonata, Orthoptera, Lepidoptera, and Reptilia. We analysed data of 134 species on a 1×1 km-grid base, collected in the last 20 years from the Netherlands, combining standardised data and opportunistic data. We applied dynamic site-occupancy models and used the results as input for analyses of (i) trends in distribution patterns, (ii) the effect of temperature on colonisation and persistence probability, and (iii) the effect of years with extreme weather on all the three metapopulation metrics. All groups, except butterflies, showed more positive than negative trends in metapopulation metrics. We did not find evidence that the probability of colonisation or persistence increases with temperature nor that extreme weather events are reflected in higher extinction risks. We could not prove that weather extremes have visible and consistent negative effects on ectothermic species in temperate northern hemisphere. These findings do not confirm the general prediction that increased weather variability imperils biodiversity. We conclude that weather extremes might not be ecologically relevant for the majority of species. Populations might be buffered against weather variation (e.g. by habitat heterogeneity), or other factors might be masking the effects (e.g. availability and quality of habitat). Consequently, we postulate that weather extremes have less, or different, impact in real world metapopulations than theory and models suggest.
    A global assembly of adult female mosquito mark-release-recapture data to inform the control of mosquito-borne pathogens
    Guerra, C.A. ; Reiner Jr, R.C. ; Perkins, T.A. ; Lindsay, S.W. ; Midega, J.T. ; Brady, O.J. ; Barker, C.M. ; Reisen, W.K. ; Harrington, L.C. ; Takken, W. ; Kitron, U. ; Lloyd, A.L. ; Hay, S.I. ; Scott, T.W. ; Smith, D.L. - \ 2014
    Parasites & Vectors 7 (2014). - ISSN 1756-3305 - 15 p.
    dominant anopheles vectors - plasmodium-falciparum transmission - distribution maps - bionomic precis - human malaria - sensitivity-analysis - population-dynamics - mathematical-model - aedes-aegypti - culicidae
    Background Pathogen transmission by mosquitos is known to be highly sensitive to mosquito bionomic parameters. Mosquito mark-release-recapture (MMRR) experiments are a standard method for estimating such parameters including dispersal, population size and density, survival, blood feeding frequency and blood meal host preferences. Methods We assembled a comprehensive database describing adult female MMRR experiments. Bibliographic searches were used to build a digital library of MMRR studies and selected data describing the reported outcomes were extracted. Results The resulting database contained 774 unique adult female MMRR experiments involving 58 vector mosquito species from the three main genera of importance to human health: Aedes, Anopheles and Culex. Crude examination of these data revealed patterns associated with geography as well as mosquito genus, consistent with bionomics varying by species-specific life history and ecological context. Recapture success varied considerably and was significantly different amongst genera, with 8, 4 and 1% of adult females recaptured for Aedes, Anopheles and Culex species, respectively. A large proportion of experiments (59%) investigated dispersal and survival and many allowed disaggregation of the release and recapture data. Geographic coverage was limited to just 143 localities around the world. Conclusions This MMRR database is a substantial contribution to the compilation of global data that can be used to better inform basic research and public health interventions, to identify and fill knowledge gaps and to enrich theory and evidence-based ecological and epidemiological studies of mosquito vectors, pathogen transmission and disease prevention. The database revealed limited geographic coverage and a relative scarcity of information for vector species of substantial public health relevance. It represents, however, a wealth of entomological information not previously compiled and of particular interest for mosquito-borne pathogen transmission models.
    Coupling socio-economic factors and eco-hydrological processes using a cascade-modeling approach
    Odongo, V.O. ; Mulatu, D.W. ; Muthoni, F.K. ; Oel, P.R. van; Meins, F.M. ; Tol, C. van der; Skidmore, A.K. ; Groen, T.A. ; Becht, R. ; Onyando, J.O. ; Veen, A. van der - \ 2014
    Journal of Hydrology 518 (2014)Part A. - ISSN 0022-1694 - p. 49 - 59.
    land-use change - murray-darling basin - lake naivasha - population-dynamics - water availability - stream ecosystems - human impact - east-africa - kenya - rainfall
    Most hydrological studies do not account for the socio-economic influences on eco-hydrological processes. However, socio-economic developments often change the water balance substantially and are highly relevant in understanding changes in hydrological responses. In this study a multi-disciplinary approach was used to study the cascading impacts of socio-economic drivers of land use and land cover (LULC) changes on the eco-hydrological regime of the Lake Naivasha Basin. The basin has recently experienced substantial LULC changes exacerbated by socio-economic drivers. The simplified cascade models provided insights for an improved understanding of the socio-ecohydrological system. Results show that the upstream population has transformed LULC such that runoff during the period 1986–2010 was 32% higher than during the period 1961–1985. Cut-flower export volumes and downstream population growth explain 71% of the water abstracted from Lake Naivasha. The influence of upstream population on LULC and upstream hydrological processes explained 59% and 30% of the variance in lake storage volumes and sediment yield respectively. The downstream LULC changes had significant impact on large wild herbivore mammal species on the fringe zone of the lake. This study shows that, in cases where observed socio-economic developments are substantial, the use of a cascade-modeling approach, that couple socio-economic factors to eco-hydrological processes, can greatly improve our understanding of the eco-hydrological processes of a catchment.
    Effect of tillage on earthworms over short- and medium-term in conventional and organic farming
    Crittenden, S. ; Eswaramurthy, T. ; Goede, R.G.M. de; Brussaard, L. ; Pulleman, M.M. - \ 2014
    Applied Soil Ecology 83 (2014). - ISSN 0929-1393 - p. 140 - 148.
    cropping systems - soil-structure - population-dynamics - communities - diversity - abundance - lumbricidae - landscapes - compaction - management
    Earthworms play an important role in many soil functions and are affected by soil tillage in agricultural soils. However, effects of tillage on earthworms are often studied without considering species and their interactions with soil properties. Furthermore, many field studies are based on one-time samplings that do not allow for characterisation of temporal variation. The current study monitored the short (up to 53 days) and medium term (up to 4 years) effects of soil tillage on earthworms in conventional and organic farming. Earthworm abundances decreased one and three weeks after mouldboard ploughing in both conventional and organic farming, suggesting direct and indirect mechanisms. However, the medium-term study revealed that earthworm populations in mouldboard ploughing systems recovered by spring. The endogeic species Aporrectodea caliginosa strongly dominated the earthworm community (76%), whereas anecic species remained
    The impact of large herbivores on woodland–grassland dynamics in fragmented landscapes: The role of spatial configuration and disturbance
    Schippers, P. ; Teeffelen, A.J.A. van; Verboom-Vasiljev, J. ; Vos, C.C. ; Kramer, K. ; Wallis de Vries, M.F. - \ 2014
    Ecological Complexity 17 (2014). - ISSN 1476-945X - p. 20 - 31.
    north temperate forests - red deer - population-dynamics - metapopulation dynamics - habitat fragmentation - distribution patterns - grazing systems - management - regeneration - resilience
    The vegetation structure of natural ecosystems is usually considered independent of their size and their location in the landscape. In this study, we examine the effect of size, spatial configuration and disturbances on the dynamic interactions of large herbivores and vegetation in a patchy environment using a metapopulation model. Simulations indicate that small, isolated or unfenced patches have low herbivore numbers and high tree cover whereas large, well-connected or fenced patches support high herbivore densities and are covered by grassland. Recovery of both herbivore numbers and forest cover in response to disturbance is slow (>100 years). These long recovery times are partly attributable to negative feedbacks between herbivore numbers and tree cover. When the population of large herbivores is disturbed, forest is able to expand, subsequently inhibiting herbivore population recovery. Likewise, forest disturbance allows herbivore population expansion, which inhibits forest recovery. Additionally, infrequent and limited disturbances like hunting and forest removal also affect the vegetation cover in patches of nature. Thus, our work indicates that the location and size of patches, together with disturbances, largely determine the structure of the vegetation in fragmented landscapes
    Infectious disease agents mediate interaction in food webs and ecosystems
    Selaković, S. ; Ruiter, P.C. de; Heesterbeek, J.A.P. - \ 2014
    Proceedings of the Royal Society. B: Biological Sciences 281 (2014)1777. - ISSN 0962-8452 - 11 p.
    biological-control - population-dynamics - species-diversity - mustela-nigripes - canine-distemper - african lions - host behavior - coral-reef - parasites - communities
    Infectious agents are part of food webs and ecosystems via the relationship with their host species that, in turn, interact with both hosts and non-hosts. Through these interactions, infectious agents influence food webs in terms of structure, functioning and stability. The present literature shows a broad range of impacts of infectious agents on food webs, and by cataloguing that range, we worked towards defining the various mechanisms and their specific effects. To explore the impact, a direct approach is to study changes in food-web properties with infectious agents as separate species in the web, acting as additional nodes, with links to their host species. An indirect approach concentrates not on adding new nodes and links, but on the ways that infectious agents affect the existing links across host and non-host nodes, by influencing the 'quality' of consumer-resource interaction as it depends on the epidemiological state host involved. Both approaches are natural from an ecological point of view, but the indirect approach may connect more straightforwardly to commonly used tools in infectious disease dynamics.
    Sclerotium rolfsii dynamics in soil as affected by crop sequences
    Leoni, C. ; Braak, C.J.F. ter; Gilsanz, J.C. ; Dogliotti, S. ; Rossing, W.A.H. ; Bruggen, A.H.C. van - \ 2014
    Applied Soil Ecology 75 (2014). - ISSN 0929-1393 - p. 95 - 105.
    southern blight - vegetable farms - soilborne pathogens - population-dynamics - organic amendments - north-carolina - management - rotations - survival - residues
    Crop rotation has been used for the management of soilborne diseases for centuries, but has not often been planned based on scientific knowledge. Our objective was to generate information on Sclerotium rolfsii dynamics under different crop or intercrop activities, and design and test a research approach where simple experiments and the use of models are combined to explore crop sequences that minimize Southern blight incidence. The effect of seventeen green manure (GM) amendments on sclerotia dynamics was analyzed in greenhouse and field plot experiments during two years. The relative densities of viable sclerotia 90 days after winter GM (WGM) incorporation were generally lower than after summer GM (SGM) incorporation, with average recovery values of 60% and 61% for WGM in the field, 66% and 43% for WGM in the greenhouse, and 162% to 91% for SGM in the greenhouse, in 2009 and 2010, respectively. Sclerotia survival on day d after GM amendment was described by the model Sf = Si × exp(-b × d), relating initial (Si) and final (Sf) sclerotia densities. Relative decay rates of the sclerotia (b) in SGM amended soil were largest for alfalfa (0.0077 ± 0.0031 day-1) and sudangrass (0.0072 ± 0.0030 day-1). In WGM amended soil, the largest b values were for oat (0.0096 ± 0.0024 day-1), wheat (0.0090 ± 0.0024 day-1) and alfalfa (0.0087 ± 0.0023 day-1). The effect of three cropping sequences (sweet pepper–fallow, sweet pepper–black oat and sweet pepper–onion) on sclerotia dynamics was analyzed in microplot experiments, and the data were used to calibrate the model Pf = Pi/(a + ßPi), relating initial (Pi) and final (Pf) sclerotia densities. Median values for the relative rate of population increase at low Pi (1/a, dimension less) and the asymptote (1/ß, number of viable sclerotia in 100 g of dry soil) were 8.22 and 4.17 for black oat (BO), 1.13 and 8.64 for onion (O), and 6.26 and 17.93 for sweet pepper (SwP). By concatenating the two models, sclerotia population dynamics under several crop sequences were simulated. At steady state, the sequence SwP–O–Fallow–BO resulted in the lowest long-term sclerotia density (7.09 sclerotia/100 g soil), and SwP–Fallow in the highest (17.89 sclerotia/100 g soil). The developed methodology facilitates the selection of a limited number of rotation options to be tested in farmers’ fields.
    Forage fish, their fisheries and their predators: who drives whom?
    Engelhard, G.H. ; Peck, M.A. ; Rindorf, A. ; Smout, S.C. ; Deurs, M. van; Raab, K.E. ; Andersen, K.H. ; Garthe, S. ; Lauerburg, R.A.M. ; Scott, F. ; Brunel, T.P.A. ; Aarts, G.M. ; Kooten, T. van; Dickey-Collas, M. - \ 2014
    ICES Journal of Marine Science 71 (2014)1. - ISSN 1054-3139 - p. 90 - 104.
    herring clupea-harengus - sprat sprattus-sprattus - sandeel ammodytes-marinus - ecosystem-based management - pout trisopterus-esmarkii - cod gadus-morhua - north-sea fish - population-dynamics - trophic cascades - environmental variability
    The North Sea has a diverse forage fish assemblage, including herring, targeted for human consumption; sandeel, sprat, and Norway pout, exploited by industrial fisheries; and some sardine and anchovy, supporting small-scale fisheries. All show large abundance fluctuations, impacting on fisheries and predators. We review field, laboratory, and modelling studies to investigate the drivers of this complex system of forage fish. Climate clearly influences forage fish productivity; however, any single-species considerations of the influence of climate might fail if strong interactions between forage fish exist, as in the North Sea. Sandeel appears to be the most important prey forage fish. Seabirds are most dependent on forage fish, due to specialized diet and distributional constraints (breeding colonies). Other than fisheries, key predators of forage fish are a few piscivorous fish species including saithe, whiting, mackerel, and horse-mackerel, exploited in turn by fisheries; seabirds and seals have a more modest impact. Size-based foodweb modelling suggests that reducing fishing mortality may not necessarily lead to larger stocks of piscivorous fish, especially if their early life stages compete with forage fish for zooplankton resources. In complex systems, changes in the impact of fisheries on forage fish may have potentially complex (and perhaps unanticipated) consequences on other commercially and/or ecologically important species.
    Fusarium oxysporum f.sp. cepae dynamics: in-plant multiplication and crop sequence simulations
    Leoni, C. ; Vries, M. de; Braak, C.J.F. ter; Bruggen, A.H.C. van; Rossing, W.A.H. - \ 2013
    European Journal of Plant Pathology 137 (2013)3. - ISSN 0929-1873 - p. 545 - 561.
    f-sp melonis - ecological intensification - verticillium-dahliae - disease suppression - population-dynamics - organic amendments - soilborne diseases - farming systems - root diseases - wilt pathogen
    To reduce Fusarium Basal Rot caused by Fusarium oxysporum f.sp. cepae (Foc) through crop rotation, plant species should be selected based on Foc multiplication in their roots. Foc multiplication rates in 13 plant species were tested in a greenhouse. All plant species enabled Foc multiplication. The lowest Foc levels (cfu g-1 dry root) were found for wheat, sunflower, cowpea and millet, the highest for black bean. The highest Foc levels per plant were calculated for sudan grass. These data were used to calibrate the model Pf¿=¿Pi/(a¿+¿ßPi) relating final (Pf) and initial (Pi) Foc levels in the soil. The rate of population increase at low Pi (1/a) was highest for onion and black oat and smallest for sunflower. The pathogen carrying capacity (1/ß) was highest for black oat and black bean, and lowest for wheat, cowpea and foxtail millet. Foc soil population dynamics was simulated for crop sequences by concatenating Pi-Pf values, considering instantaneous or gradual pathogen release after harvest. Different soil Foc populations were attained after reaching steady states. Foc populations in the sequence onion –foxtail millet - wheat – cowpea were 67 % lower than in the sequence onion – sudan grass - black oat - black beans. In this work, by combining detailed greenhouse experiments with modelling, we were able to screen crops for their ability to increase Foc population and to explore potential crop sequences that may limit pathogen build-up
    Understanding the effects of a new grazing policy: the impact of seasonal grazing on shrub demography in the Inner Mongolian steppe
    Li, Shou-Li ; Yu, F.H. ; Werger, M.J.A. ; Dong, M. ; Ramula, S. ; Zuidema, P.A. - \ 2013
    Journal of Applied Ecology 50 (2013)6. - ISSN 0021-8901 - p. 1377 - 1386.
    integral projection models - herb lathyrus-vernus - population-dynamics - environmental stochasticity - semiarid savanna - elasticities - performance - plants - restoration - variability
    1.Grazing by livestock is a common land use in arid and semi-arid areas. Developing sustainable grazing regimes that conserve vegetation and maintain productivity is therefore important in these ecosystems. To solve environmental problems induced by overgrazing in Chinese semi-arid regions, the Chinese government has recently implemented a new policy of seasonal grazing, with no grazing from April to July. While this policy has been implemented in huge areas, its consequences for grazed plant populations have not been assessed so far. 2.We evaluated the demographic consequences of seasonal grazing for Caragana intermedia, a long-lived dominant shrub serving as a main food source for livestock in Inner Mongolia, China. Controlled seasonally grazed and ungrazed populations were monitored during 2007–2009, and their vital rates were compared. We then constructed integral projection models (IPMs) to analyse the effects of seasonal grazing on population dynamics. 3.Seasonal grazing negatively affected two vital rates: seedling survival and seedling recruitment were 25–71% and 69–91% lower in the seasonally grazed treatment than in the ungrazed situation, respectively. Seasonal grazing had a minimal effect on adult survival and growth, but improved juvenile survival by 8–31%. 4.Despite its effects on several vital rates, seasonal grazing did not significantly affect long-term population growth rates (¿), which remained close to unity in both grazed and ungrazed areas based on deterministic and stochastic analyses. An elasticity analysis showed that population growth rate was mainly governed by the high survival of large adults. Results of Life Table Response Experiments (LTREs) revealed that variation in population growth rates across treatments and years was more strongly governed by temporal differences than by grazing. 5.Synthesis and applications. Our study showed that the relatively large changes in vital rates induced by seasonal grazing did not affect population growth rates. Caragana intermedia populations can be sustained under the seasonal grazing regime probably because the grazing intensity is moderate and because this species has a high probability of adult survival under grazing. Plant species with similar life-history traits to C. intermedia are likely to offer good opportunities for sustainable seasonal grazing regimes in arid and semi-arid inland ecosystems
    Can fisheries-induced evolution shift reference points for fisheries management?
    Heino, M. ; Baulier, L. ; Boukal, D.S. ; Mollet, F.M. ; Rijnsdorp, A.D. - \ 2013
    ICES Journal of Marine Science 70 (2013)4. - ISSN 1054-3139 - p. 707 - 721.
    cod gadus-morhua - north-sea plaice - life-history evolution - exploited fish stocks - pleuronectes-platessa l - eco-genetic model - atlantic cod - population-dynamics - reproductive investment - natural mortality
    Biological reference points are important tools for fisheries management. Reference points are not static, but may change when a population's environment or the population itself changes. Fisheries-induced evolution is one mechanism that can alter population characteristics, leading to “shifting” reference points by modifying the underlying biological processes or by changing the perception of a fishery system. The former causes changes in “true” reference points, whereas the latter is caused by changes in the yardsticks used to quantify a system's status. Unaccounted shifts of either kind imply that reference points gradually lose their intended meaning. This can lead to increased precaution, which is safe, but potentially costly. Shifts can also occur in more perilous directions, such that actual risks are greater than anticipated. Our qualitative analysis suggests that all commonly used reference points are susceptible to shifting through fisheries-induced evolution, including the limit and “precautionary” reference points for spawning-stock biomass, Blim and Bpa, and the target reference point for fishing mortality, F0.1. Our findings call for increased awareness of fisheries-induced changes and highlight the value of always basing reference points on adequately updated information, to capture all changes in the biological processes that drive fish population dynamics.
    Frankincense tree recruitment failed over the past half century
    Tolera Feyissa, M. ; Sass, U.G.W. ; Eshete, A. ; Bongers, F. ; Sterck, F.J. - \ 2013
    Forest Ecology and Management 304 (2013). - ISSN 0378-1127 - p. 65 - 72.
    annual growth rings - long-term growth - dry-forest trees - boswellia-papyrifera - pterocarpus-angolensis - population-dynamics - age-determination - acacia-erioloba - seed predation - tropical trees
    Boswellia papyrifera (Burseraceae) trees grow in dry woodlands south of the Sahara and produce frankincense, the economically important olio-gum resin used for cultural and religious ceremonies throughout the world and as raw material in several industries. Across its distribution area, this species is threatened by farmland expansion, fire, improper tapping and overgrazing. Most of its populations lack saplings and small-sized trees (e.g.
    European Perspectives on the Adoption of Nonchemical Weed Management in Reduced-Tillage Systems for Arable Crops
    Melander, B. ; Munier-Jolain, N.M. ; Charles, R. ; Wirth, J. ; Schwarz, J. ; Weide, R.Y. van der; Bonin, L. ; Jensen, P.K. ; Kudsk, P.K. - \ 2013
    Weed Technology 27 (2013)1. - ISSN 0890-037X - p. 231 - 240.
    thistle cirsium-arvense - population-dynamics - oilseed rape - no-till - alopecurus-myosuroides - herbicide performance - conservation tillage - cropping systems - stubble tillage - spring barley
    Noninversion tillage with tine- or disc-based cultivations prior to crop establishment is the most common way of reducing tillage for arable cropping systems with small grain cereals, oilseed rape, and maize in Europe. However, new regulations on pesticide use might hinder further expansion of reduced-tillage systems. European agriculture is asked to become less dependent on pesticides and promote crop protection programs based on integrated pest management (IPM) principles. Conventional noninversion tillage systems rely entirely on the availability of glyphosate products, and herbicide consumption is mostly higher compared to plow-based cropping systems. Annual grass weeds and catchweed bedstraw often constitute the principal weed problems in noninversion tillage systems, and crop rotations concurrently have very high proportions of winter cereals. There is a need to redesign cropping systems to allow for more diversification of the crop rotations to combat these weed problems with less herbicide input. Cover crops, stubble management strategies, and tactics that strengthen crop growth relative to weed growth are also seen as important components in future IPM systems, but their impact in noninversion tillage systems needs validation. Direct mechanical weed control methods based on rotating weeding devices such as rotary hoes could become useful in reduced-tillage systems where more crop residues and less workable soils are more prevalent, but further development is needed for effective application. Owing to the frequent use of glyphosate in reduced-tillage systems, perennial weeds are not particularly problematic. However, results from organic cropping systems clearly reveal that desisting from glyphosate use inevitably leads to more problems with perennials, which need to be addressed in future research.
    Within-patch habitat quality determines the resilience of specialist species in fragmented landscapes
    Ye, X. ; Skidmore, A.K. ; Wang, T. - \ 2013
    Landscape Ecology 28 (2013)1. - ISSN 0921-2973 - p. 135 - 147.
    metapopulation dynamics - population-dynamics - environmental variation - relative importance - isolation paradigm - extinction risk - effect size - long-term - heterogeneity - persistence
    Patch geometry and habitat quality among patches are widely recognized as important factors affecting population dynamics in fragmented landscapes. Little is known, however, about the influence of within-patch habitat quality on population dynamics. In this paper, we investigate the relative importance of patch geometry and within-patch habitat quality in determining population dynamics using a spatially explicit, agent-based model. We simulate two mobile species that differ in their species traits: one resembles a habitat specialist and the other a habitat generalist. Habitat quality varies continuously within habitat patches in space (and time). The results show that spatial variation in within-patch quality, together with patch area, controls population abundance of the habitat specialist. In contrast, the population size of the generalist species depends on patch area and isolation. Temporal variation in within-patch quality is, however, less influential in driving the population resilience of both species. We conclude that specialist species are more sensitive than generalist species to within-patch variation in habitat quality. The patch area-isolation paradigm, developed in metapopulation theory, should incorporate variation in within-patch habitat quality, particularly for habitat specialists.
    Beyond the Plankton Ecology Group (PEG) Model: Mechanisms Driving Plankton Succession
    Sommer, U. ; Adrian, R. ; Domis, L.D. ; Elser, J.J. ; Gaedke, U. ; Ibelings, B. ; Jeppesen, E. ; Lürling, M.F.L.L.W. ; Molinero, J.C. ; Mooij, W.M. ; Donk, E. van; Winder, M. - \ 2012
    Annual Review of Ecology, Evolution, and Systematics 43 (2012)7. - ISSN 1543-592X - p. 429 - 448.
    phytoplankton spring bloom - fresh-water phytoplankton - critical depth hypothesis - clear-water - long-term - lake constance - climate-change - population-dynamics - food quality - deep lake
    UV/H2O2 treatment can be part of the process converting surface water to drinking water, but would pose a potential problem when resulting in genotoxicity. This study investigates the genotoxicity of samples collected from the water treatment plant Andijk, applying UV/H2O2 treatment with an electrical energy dose of 0.54 kWh/m(3) and a H2O2 dose of 6 mg/l. Genotoxicity was tested in vitro using the Ames and Comet assay. All samples showed negative results. Samples were also tested in in vivo genotoxicity tests in Eastern mudminnow fish (Umbra pygmaea) by a sister chromatid exchange (SCE) and a Comet assay. No significant increases in SCEs were observed, but gill cells isolated from fish exposed to water obtained immediately after UV/H2O2 treatment and to Lake IJsselmeer water showed significantly increased DNA damage in the Comet assay. All other samples tested negative in this Comet assay. This indicates that DNA damaging compounds may result from the UV/H2O2 treatment, but also that these can be efficiently eliminated upon granular activated carbon (GAC) treatment of the water. It is concluded that when combined with this subsequent GAC treatment, UV/H2O2 treatment for the production of drinking water from surface water is not of concern with respect to genotoxicity.
    Prey temporarily escape from predation in the presence of a second prey species
    Maanen, R. van; Messelink, G.J. ; Holstein, R. van; Sabelis, M.W. ; Janssen, A. - \ 2012
    Ecological Entomology 37 (2012)6. - ISSN 0307-6946 - p. 529 - 535.
    mediated apparent competition - biological-control agents - western flower thrips - phytoseiid predators - tetranychus-urticae - amblyseius-swirskii - alternative prey - frankliniella-occidentalis - generalist predator - population-dynamics
    1. Indirect interactions between populations of different prey species mediated by a shared predator population are known to affect prey dynamics. 2. Depending on the temporal and spatial scale, these indirect interactions may result in positive (apparent mutualism), neutral or negative effects (apparent competition) of the prey on each other's densities. Although there is ample evidence for the latter, evidence for apparent mutualism is scarce. 3. The effectiveness of using one species of predator for biological control of more than one pest species depends on the occurrence of such positive or negative effects. 4. We used an experimental system consisting of the two prey species Western flower thrips (Franklineilla occidentalis Pergande) and greenhouse whitefly (Trialeurodes vaporariorum Westwood) and a shared predator, the phytoseiid mite Amblyseius swirskii Athias-Henriot. We released all three species on the same plant and studied their dynamics and distribution along rows of plants. 5. We expected that the more mobile prey species (thrips) would escape temporarily in the presence of the other prey species (whitefly) by dispersing from plants with the predator. The predator was expected to disperse slower in the presence of two prey species because of the higher availability of food. 6. Evidence was found for slower dispersal of predators and short-term escape of thrips from predation when whiteflies were present, thus confirming the occurrence of short-term apparent mutualism. 7. The apparent mutualism resulted in a cascade to the first trophic level: a higher proportion of fruits was damaged by thrips in the presence of whiteflies. 8. We conclude that apparent mutualism can be an important phenomenon in population dynamics, and can significantly affect biological control of pest species that share a natural enemy.
    Circumstantial evidence for an increase in the total number and activity of borrelia-infected ixodes ricinus in the Netherlands.
    Sprong, H. ; Hofhuis, A. ; Gassner, F. ; Takken, W. ; Jacobs, F. ; Vliet, A.J.H. van; Ballegooijen, M. van; Giessen, J. van der; Takumi, K. - \ 2012
    Parasites & Vectors 5 (2012)5. - ISSN 1756-3305 - 11 p.
    tick-borne diseases - burgdorferi sensu-lato - owls strix-aluco - lyme borreliosis - population-dynamics - ixodidae nymphs - endemic area - acari - ecology - risk
    BACKGROUND: Between 1994 and 2009, a threefold increase has been observed in consultations of general practitioners for tick bites and Lyme disease in The Netherlands. The objective of this study was to determine whether an increase in the number of questing ticks infected with B. burgdorferi sensu lato is a potential cause of the rise in Lyme disease incidence. METHODS: Historic data on land usage, temperature and wildlife populations were collected and analyzed together with data from two longitudinal field studies on density of questing ticks. Effective population sizes of Borrelia burgdorferi s.l. were calculated. RESULTS: Long-term trend analyses indicated that the length of the annual tick questing season increased as well as the surface area of tick-suitable habitats in The Netherlands. The overall abundances of feeding and reproductive hosts also increased. Mathematical analysis of the data from the field studies demonstrated an increase in mean densities/activities of questing ticks, particularly of larvae between 2006 and 2009. No increase in infection rate of ticks with Borrelia burgdorferi sensu lato was found. Population genetic analysis of the collected Borrelia species points to an increase in B. afzelii and B. garinii populations. CONCLUSIONS: Together, these findings indicate an increase in the total number of Borrelia-infected ticks, providing circumstantial evidence for an increase in the risk of acquiring a bite of a tick infected with B. burgdorferi s.l. Due to the high spatiotemporal variation of tick densities/activities, long-term longitudinal studies on population dynamics of I. ricinus are necessary to observe significant trends.
    Declines amongst breeding Eider Somateria mollissima numbers in the Baltic/Wadden Sea flyway
    Ekroos, J. ; Fox, A.D. ; Christensen, T.K. ; Cervencl, A. - \ 2012
    Ornis Fennica 89 (2012). - ISSN 0030-5685 - p. 81 - 90.
    population-dynamics - spring migration - wadden sea - long-term - age
    We report on the status of theBaltic/Wadden Sea flyway Eider population based on trends in breeding and wintering numbers throughout the region, supplemented by changes in the sex ratio and proportion of young Eiders as monitored in the Danish hunting bag. At the flyway scale, total numbers of breeding pairs decreased by 48% during 2000–2009, after relatively stable breeding numbers in 1991–2000. The majority of the population nest in Finland and Sweden,where the number of breeding pairs has halved over the same period. After initial declines in winter numbers between 1991 and 2000, during 2000–2009, national wintering numbers increased in the Baltic Sea, but decreased in the Wadden Sea. The annual proportion of adult females in the Danish hunting bag data de creased from ca.45%(1982) to ca.25%(2009) and simultaneously the proportion of firstwinter birds fell from ca. 70% to ca. 30%, indicating dramatic structural changes in the Danish wintering numbers. These results suggest that the total flyway populationwill experience further declines, unless productivity increases and the factors responsible for decreasing adult female survival are identified and ameliorated.We discuss potential population drivers and present some recommendations for improved flyway-levelmonitoring and management of Eiders.
    Assessing non-target effects and host feeding of the exotic parasitoid Apanteles taragamae, a potential biological control agent of the cowpea pod borer Maruca vitrata
    Dannon, A.E. ; Tamo, M. ; Huis, A. van; Dicke, M. - \ 2012
    BioControl 57 (2012)3. - ISSN 1386-6141 - p. 415 - 425.
    busseola-fusca lepidoptera - larval parasitoids - intrinsic competition - lethal interference - population-dynamics - natural enemies - arthropod pests - hymenoptera - braconidae - pyralidae
    Apanteles taragamae Viereck is a larval parasitoid introduced in Benin for classical biological control of the cowpea pod borer Maruca vitrata Fabricius. In the laboratory, we evaluated the effects of A. taragamae on non-target herbivore species, and on another parasitoid of M. vitrata, i.e. the egg-larval parasitoid Phanerotoma leucobasis Kriechbaumer. Furthermore, we addressed the host feeding behaviour of A. taragamae. The host specificity of A. taragamae was assessed by offering six other lepidopteran species to the wasp. The competitive ability of A. taragamae was studied by providing the wasp with one- and two-days-old M. vitrata larvae that had hatched from eggs previously parasitized by P. leucobasis. Controls consisted of eggs and larvae offered only to P. leucobasis and A. taragamae, respectively. None of the other six lepidopteran species was successfully parasitized by A. taragamae. The larval parasitoid A. taragamae outcompeted the egg-larval parasitoid P. leucobasis when offered two-days-old host larvae. Competition between the two parasitoid species did not significantly affect one-day-old host larvae that were less suitable to A. taragamae. Host feeding by A. taragamae did not affect survival of one-day-old or two-days-old M. vitrata larvae. However, the percentage parasitism of two-days-old larvae was significantly reduced when exposed to female A. taragamae wasps that had been starved during 48 h. The data are discussed with regard to host specificity, host feeding patterns and to factors underlying the outcome of intrinsic competition between parasitoid species.
    Site-specific distribution of the bivalve Scrobicularia plana along the European coast
    Santos, S. ; Aarts, G.M. ; Luttikhuizen, P. ; Campos, J. ; Piersma, T. ; Veer, H.W. van der - \ 2012
    Marine Ecology Progress Series 471 (2012). - ISSN 0171-8630 - p. 123 - 134.
    spatial-distribution patterns - wadden sea - environmental variables - estuarine macrobenthos - population-dynamics - landscape-scale - food-web - invertebrates - community - ecology
    The development and maintenance of spatial patterns and the way they affect the dynamics of populations and ecosystems is a key issue in ecology. Since each individual and each species experiences the environment on a unique range of scales, it is vital to determine the spatial scales across which organisms interact with each other and the structuring influence of their environments, which can be achieved by analyzing species’ distribution patterns. Here, the spatial variation in the distribution of Scrobicularia plana is described for 4 intertidal areas along the species’ distributional range. Spatial autocorrelation correlograms based on Moran’s coefficient reveal that while the Trondheim (Norway) population was randomly distributed, at Minho (Portugal), the Westerschelde, and the Wadden Sea (both in The Netherlands) populations were aggregated. Patch diameter varied from 150 to 1250 m, in Minho and Westerschelde, respectively; while in the Wadden Sea, patches of 4 to 10 km were detected. Comparisons of spatial patterns with those of other co-occurring bivalve species (Abra tenuis, Cerastoderma edule, and Macoma balthica) revealed that S. plana’s distribution was generally patchier. The distribution of S. plana was correlated with sediment type at Westerschelde and Trondheim, but not Minho. The observed differences in distribution patterns and their correlation with environmental factors reveal that spatial patterns of S. plana are site-specific rather than species-specific.
    Dietary overlap between the potential competitors herring, sprat and anchovy in the North Sea
    Raab, K.E. ; Nagelkerke, L.A.J. ; Boeree, C. ; Rijnsdorp, A.D. ; Temming, A. ; Dickey-Collas, M. - \ 2012
    Marine Ecology Progress Series 470 (2012). - ISSN 0171-8630 - p. 101 - 111.
    engraulis-encrasicolus l. - central baltic sea - clupea-harengus - feeding-behavior - intraguild predation - trophic interactions - population-dynamics - mediterranean sea - fish eggs - irish sea
    European anchovy Engraulis encrasicolus increased its abundance and distribution in the North Sea during the mid-1990s and may consume similar zooplankton to and/or compete with other occupants of the North Sea like herring Clupea harengus and sprat Sprattus sprattus. The diets of adult anchovy, sprat and juvenile herring of comparable sizes, sampled close in time and space, were compared to understand how the 3 species prey on zooplankton and establish whether their diets overlap or not. Anchovy was found to be more generalist, consuming a higher diversity of prey items. Herring was more specialized, with low diversity of food items. Sprat was intermediate between anchovy and herring. The dietary overlap between anchovy and sprat was highest, followed by herring and sprat before anchovy and herring. The mean weight of stomach contents did not differ between species. We conclude that of the 3 species, anchovy is likely to be the least affected by changing plankton communities.
    Variation in ploidy level and phenology can result in large and unexpected differences in demography and climatic sensitivity between closely related ferns.
    Groot, G.A. de; Zuidema, P.A. ; Groot, H. ; During, H.J. - \ 2012
    American Journal of Botany 99 (2012)8. - ISSN 0002-9122 - p. 1375 - 1387.
    inbreeding depression - polystichum-acrostichoides - population-dynamics - life - pteridophyta - polyploidy - plants - dryopteridaceae - components - evolution
    • Premise of the study: Current environmental changes may affect the dynamics and viability of plant populations. This environmental sensitivity may differ between species of different ploidy level because polyploidization can influence life history traits. We compared the demography and climatic sensitivity of two closely related ferns: the tetraploid Polystichum aculeatum and one of its diploid parents, Polystichum setiferum. • Methods: Matrix models were used to assess the effects of life history variation on population dynamics under varying winter conditions. We analyzed the contributions of all key aspects of the fern life cycle to population growth. Our study is the first to also include the gametophyte generation. • Key results: Projected population growth rate (¿) was much higher for the tetraploid P. aculeatum (1.516) than for P. setiferum (1.071) under normal winter conditions. During a year with harsh winter conditions, population growth of P. aculeatum was strongly reduced. This finding contradicts our expectation that the winter-hardy fronds of this species would allow high survival of harsh winters. Differences in ¿ between species and between years with different winter conditions were mostly caused by variation in gametophyte-related recruitment rates, a finding that shows the importance of including gametophytes in fern demographic studies. • Conclusions: Our results indicate that populations of closely related ferns can show large differences in population performance, mainly related to recruitment rates and frond phenology, and that these differences may depend greatly on climatic conditions. Our findings provide a first indication that (allo)polyploidization in ferns can have a significant effect on population dynamics.
    Resistance to Bemisia tabaci in tomato wild relatives
    Firdaus, S. ; Heusden, A.W. van; Hidayati, N. ; Supena, E.D.J. ; Visser, R.G.F. ; Vosman, B. - \ 2012
    Euphytica 187 (2012)1. - ISSN 0014-2336 - p. 31 - 45.
    hirsutum-f-glabratum - whitefly trialeurodes-vaporariorum - lycopersicon-hirsutum - argentifolii homoptera - population-dynamics - glandular trichomes - insect-resistance - spodoptera-exigua - feeding-behavior - pest resistance
    Bemisia tabaci is one of the most threatening pests in agriculture, particularly in Solanaceous crops such as tomato and pepper that are cultivated in the open field. Pesticide application is often not effective and hazardous to humans and environment. The exploitation of plant natural defenses that are present in wild relatives of tomato, may offer a solution. To evaluate resistance parameters and to identify plant material with high levels of resistance, we screened a number of accessions of tomato wild relatives using three methods; a free-choice test in a screenhouse in Indonesia, a no-choice test with clip-on cages in a greenhouse and a leaf disc test in a climate-room in the Netherlands. Antibiosis resulting in low adult survival was the major component for resistance in tomato. However, other resistance component(s) may play a role as well. In some accessions there was a change in the resistance level over time. Several resistance parameters used in the different tests were well correlated. The best resistance source was an accession of Solanum galapagense, which had not been identified as being resistant in the past. This is of particular interest as this species is closely related to the cultivated tomato, which may facilitate introgression of the resistance component(s). Whitefly non-preference and resistance were associated with the presence of type IV trichomes. Other mechanisms might be involved since some accessions without type IV trichomes showed low nymphal density. The leaf disc test is a good in vitro alternative for the clip-on cage whitefly resistance screening, as shown by the high correlation between the results obtained with this test and the clip-on cage test. This offers breeders the possibility to carry out tests more efficiently
    The Association of Antarctic Krill Euphausia superba with the Under-Ice Habitat
    Florentino De Souza Silva, A.P. ; Franeker, J.A. van; Siegel, V. ; Haraldsson, M. ; Strass, V. ; Meesters, H.W.G. ; Bathmann, U. ; Wolff, W.J. - \ 2012
    PLoS ONE 7 (2012)2. - ISSN 1932-6203 - 11 p.
    northern weddell sea - southern-ocean - pack-ice - community structure - lazarev sea - trophic relationships - population-dynamics - foraging behavior - elephant island - energy budgets
    The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean) during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT), which sampled the 0-2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m(-2) in summer and autumn, and 2.7 individuals m(-2) in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0-2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0-2 m layer were higher than corresponding values from the 0-200 m layer collected with Rectangular Midwater Trawls (RMT) in summer. In winter, under-ice densities far surpassed maximum 0-200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate change
    Where do egg production methods for estimating fish biomass go from here?
    Dickey-Collas, M. ; Somarakis, S. ; Witthames, P.R. ; Damme, C.J.G. van; Uriarte, A.R. ; Lo, N.C.H. ; Bernal, M. - \ 2012
    Fisheries Research 117-118 (2012). - ISSN 0165-7836 - p. 6 - 11.
    anchovy engraulis-encrasicolus - sardine sardinops-sagax - gadus-morhua-l. - pleuronectes-platessa l. - north-sea plaice - solea-solea l. - postovulatory follicles - population-dynamics - trachurus-trachurus - multinomial models
    The special theme volume of Fisheries Research is intended to synthesise the current understanding of the methods and applicability of egg production methods (EPM). It originates from a workshop in Athens which also focused on the future challenges to both the science and logistics of carrying out and using egg production methods. This synthesis addresses three interlinked challenges for those using EPM; how methods have, and need to be, improved, what added value can EPM provide directly to aid advice for management of the marine environment and lastly what extra understanding can EPM bring to marine science? EPM surveys offer some of the most intensive sampling of plankton and adult fish populations in fisheries science. They provide, and will probably provide further insights into fish reproductive processes, embryonic development and spatial and temporal variability in fish populations. Researchers should be encouraged to examine new methods for representative real-time sampling, swift processing of samples and integration of sampling of adults and plankton. EPM provides managers with many “added value” products on habitats and spawning and already provides platforms for monitoring hydrography, zooplankton distributions and acoustic back scatter. Some EPM surveys also incorporate monitoring of birds and sea mammals. EPM, together with aquaculture, has progressed understanding of fish reproductive biology and embryo development. EPM provides long time series of both the ichthyoplankton and fish reproductive traits thus enabling informed study of regime change, variability and ecosystem status. As the EPM become more developed, we expect that these contributions to marine science will increase
    Predicting the effect of climate change on African trypanosomiasis: integrating epidemiology with parasite and vector biology
    Moore, S. ; Shrestha, S. ; Tomlinson, K.W. ; Vuong, H. - \ 2012
    Journal of the Royal Society, Interface 9 (2012)70. - ISSN 1742-5689 - p. 817 - 830.
    rhodesiense sleeping sickness - morsitans morsitans diptera - sensed vegetation data - south-eastern uganda - common fly belt - infectious-diseases - glossina-morsitans - brucei-rhodesiense - tsetse-flies - population-dynamics
    Climate warming over the next century is expected to have a large impact on the interactions between pathogens and their animal and human hosts. Vector-borne diseases are particularly sensitive to warming because temperature changes can alter vector development rates, shift their geographical distribution and alter transmission dynamics. For this reason, African trypanosomiasis (sleeping sickness), a vector-borne disease of humans and animals, was recently identified as one of the 12 infectious diseases likely to spread owing to climate change. We combine a variety of direct effects of temperature on vector ecology, vector biology and vector–parasite interactions via a disease transmission model and extrapolate the potential compounding effects of projected warming on the epidemiology of African trypanosomiasis. The model predicts that epidemics can occur when mean temperatures are between 20.78C and 26.18C. Our model does not predict a large-range expansion, but rather a large shift of up to 60 per cent in the geographical extent of the range. The model also predicts that 46–77 million additional people may be at risk of exposure by 2090. Future research could expand our analysis to include other environmental factors that influence tsetse populations and disease transmission such as humidity, as well as changes to human, livestock and wildlife distributions. The modelling approach presented here provides a framework for using the climate-sensitive aspects of vector and pathogen biology to predict changes in disease prevalence and risk owing to climate change.
    The role of ecological models in linking ecological risk assessment to ecosystem services in agroecosystems
    Galic, N.G. ; Schmolke, A. ; Forbes, V. ; Baveco, J.M. ; Brink, P.J. van den - \ 2012
    Science of the Total Environment 415 (2012). - ISSN 0048-9697 - p. 93 - 100.
    shallow lakes - population-dynamics - potential application - decision-making - economic value - land-use - honeybee - chemicals - wildlife - biomanipulation
    Agricultural practices are essential for sustaining the human population, but at the same time they can directly disrupt ecosystem functioning. Ecological risk assessment (ERA) aims to estimate possible adverse effects of human activities on ecosystems and their parts. Current ERA practices, however, incorporate very little ecology and base the risk estimates on the results of standard tests with several standard species. The main obstacles for a more ecologically relevant ERA are the lack of clear protection goals and the inherent complexity of ecosystems that is hard to approach empirically. In this paper, we argue that the ecosystem services framework offers an opportunity to define clear and ecologically relevant protection goals. At the same time, ecological models provide the tools to address ecological complexity to the degree needed to link measurement endpoints and ecosystem services, and to quantify service provision and possible adverse effects from human activities. We focus on the ecosystem services relevant for agroecosystem functioning, including pollination, biocontrol and eutrophication effects and present modeling studies relevant for quantification of each of the services. The challenges of the ecosystem services approach are discussed as well as the limitations of ecological models in the context of ERA. A broad, multi-stakeholder dialog is necessary to aid the definition of protection goals in terms of services delivered by ecosystems and their parts. The need to capture spatio-temporal dynamics and possible interactions among service providers pose challenges for ecological models as a basis for decision making. However, we argue that both fields are advancing quickly and can prove very valuable in achieving more ecologically relevant ERA.
    Toxicokinetic-toxicodynamic modeling of quantal and graded sublethal endpoints: a brief discussion of concepts
    Ashauer, R. ; Agatz, A. ; Albert, C. ; Ducrot, V. ; Galic, N.G. ; Hendriks, J. ; Jager, T. ; Kretschmann, A. ; O'Connor, I. ; Rubach, M.N. ; Nyman, M. ; Schmitt, W. ; Stadnicka, J. ; Brink, P.J. van den - \ 2011
    Environmental Toxicology and Chemistry 30 (2011)11. - ISSN 0730-7268 - p. 2519 - 2524.
    time-varying concentrations - biology-based approach - gammarus-pulex - daphnia-magna - population-dynamics - organic-chemicals - mixture toxicity - pulsed exposure - binary-mixtures - hyalella-azteca
    We report on the advantages and problems of using toxicokinetic-toxicodynamic (TKTD) models for the analysis, understanding, and simulation of sublethal effects. Only a few toxicodynamic approaches for sublethal effects are available. These differ in their effect mechanism and emphasis on linkages between endpoints. We discuss how the distinction between quantal and graded endpoints and the type of linkage between endpoints can guide model design and selection. Strengths and limitations of two main approaches and possible ways forward are outlined
    Termite and earthworm abundance and taxonomic richness under long-term conservation soil management in Saria, Burkina Faso, West Africa
    Zida, Z. ; Ouedraogo, E. ; Mando, A. ; Stroosnijder, L. - \ 2011
    Applied Soil Ecology 51 (2011)11. - ISSN 0929-1393 - p. 122 - 129.
    organic-matter - agricultural intensification - agroecosystem function - population-dynamics - tropical forests - carbon dynamics - feeding termite - land-use - biodiversity - diversity
    Unsustainable crop and soil management practices are major causes of soil degradation and declining soil biodiversity in West Africa. Identifying soil management practices that favor macrofauna abundance is highly desirable for long-term soil health. This study investigates the effects of long-term conservation soil management on termite and earthworm abundance and taxonomic richness in the central plateau of Burkina Faso. Trials included rotations with 5 Mg ha-1 yr-2 of organic matter added (established in 1960), application of 10 Mg ha-1 yr-1applied with additional organic (manure or straw) and mineral inputs (established in 1980) and different tillage systems (established in 1990) where 10 Mg ha-1 yr-1 of organic matter was also applied. Soil macrofauna was surveyed at the soil surface and in the upper 30 cm using transect and monolith sampling methods, eight weeks after sorghum crop planting. A total of five termite taxa: Trinervitermes sp., Microtermes sp., Odontotermes magdalenae, Macrotermes sp. and Amitermes stephensoni; belonging to the family of Termitidae, and two earthworm taxa: Dichogaster affinis, Millsonia inermis; from the family of Acanthodrilidae were found. Termite taxonomic richness per treatment ranged between 1 and 4, while earthworm taxa ranged from 0 to 2. Under rotation, one termite taxa and no earthworm taxa were identified. In the organic amendment plots, three termite and two earthworm taxa were found. And light tillage (animal or hand) resulted in four termite taxa and one earthworm taxa. The two types of fauna clearly responded differently to the different conservation soil management practices. Under rotation lower recorded macrofauna population was attributed to the lower rate of applied organic matter compared to levels applied in the organic amendment and tillage trials and where more macrofauna were found. Location of food stock (rooting depth of different crops in the rotation) also had a significant effect on termite presence. Effect of rooting depth on earthworms was not observable due to the absence of earthworms in the rotation trials (possibly due to insecticide application. Manure treatments favored earthworms, while sorghum straw treatments favored termites likely due to respective preference for easy versus difficult to digest organic sources. Animal plowing and hand hoeing had similar and significantly positive effects and both termite and earthworm biological components compared to tractor tillage. We conclude that termite and earthworm abundance and taxonomic richness are most significantly affected by the type and amount of organic matter applied and tillage regimes, with rooting depth of rotations crops also playing a significant role. To promote macrofauna abundance and taxonomic richness in soils, integrated conservation soil management practices with attention to the particular needs and preferences of termites and earthworms is needed.
    Resonance of plankton communities with temperature fluctuations
    Beninca, E. ; Dakos, V. ; Nes, E.H. van; Huisman, J. ; Scheffer, M. - \ 2011
    American Naturalist 178 (2011)4. - ISSN 0003-0147 - p. E85 - E95.
    colored environmental noise - predator-prey system - food-web - population-dynamics - sustained oscillations - extinction risk - chaos - time - phytoplankton - variability
    The interplay between intrinsic population dynamics and environmental variation is still poorly understood. It is known, however, that even mild environmental noise may induce large fluctuations in population abundances. This is due to a resonance effect that occurs in communities on the edge of stability. Here, we use a simple predator-prey model to explore the sensitivity of plankton communities to stochastic environmental fluctuations. Our results show that the magnitude of resonance depends on the timescale of intrinsic population dynamics relative to the characteristic timescale of the environmental fluctuations. Predator-prey communities with an intrinsic tendency to oscillate at a period T are particularly responsive to red noise characterized by a timescale of [Formula: see text]. We compare these theoretical predictions with the timescales of temperature fluctuations measured in lakes and oceans. This reveals that plankton communities will be highly sensitive to natural temperature fluctuations. More specifically, we demonstrate that the relatively fast temperature fluctuations in shallow lakes fall largely within the range to which rotifers and cladocerans are most sensitive, while marine copepods and krill will tend to resonate more strongly with the slower temperature variability of the open ocean
    Life-history traits of gaur Bos gaurus: A first analysis
    Ahrestani, F.S. ; Iyer, S. ; Heitkonig, I.M.A. ; Prins, H.H.T. - \ 2011
    Mammal Review 41 (2011)1. - ISSN 0305-1838 - p. 75 - 84.
    sexual size dimorphism - population-dynamics - prey selection - southern india - bison - ungulate - ecology - buffalo - tiger - carnivores
    In this first detailed analysis of gaur Bos gaurus life-history traits, data were collected from a 20-month field study in South India and from captive gaur populations. Mean age of females at first parturition was 3 years; females remained fertile beyond the age of 15 years. Adult females were three times more abundant than adult males in the wild; survival of females was greater than males beyond three years of age. Life span of both sexes has not exceeded 24 years in captivity. Gaur life-history traits are similar to those of other similar-sized Bovini species.
    Harvest-induced maturation evolution under different life-history trade-offs and harvesting regimes
    Poos, J.J. ; Brannstrom, A. ; Dieckman, U. - \ 2011
    Journal of Theoretical Biology 279 (2011)1. - ISSN 0022-5193 - p. 102 - 112.
    north-sea plaice - fisheries-induced evolution - herring clupea-harengus - evolving fish stocks - cod gadus-morhua - reaction norms - population-dynamics - marine reserves - brook charr - arctic cod
    The potential of harvesting to induce adaptive changes in exploited populations is now increasingly recognized. While early studies predicted that elevated mortalities among larger individuals select for reduced maturation size, recent theoretical studies have shown conditions under which other, more complex evolutionary responses to size-selective mortality are expected. These new predictions are based on the assumption that, owing to the trade-off between growth and reproduction, early maturation implies reduced growth. Here we extend these findings by analyzing a model of a harvested size-structured population in continuous time, and by systematically exploring maturation evolution under all three traditionally acknowledged costs of early maturation: reduced fecundity, reduced growth, and/or increased natural mortality. We further extend this analysis to the two main types of harvest selectivity, with an individual's chance of getting harvested depending on its size and/or maturity stage. Surprisingly, we find that harvesting mature individuals not only favors late maturation when the costs of early maturation are low, but promotes early maturation when the costs of early maturation are high. To our knowledge, this study therefore is the first to show that harvesting mature individuals can induce early maturation.
    The consequences of being colonial: Allee effects in metapopulations of seabirds
    Schippers, P. ; Stienen, E.W.M. ; Schotman, A.G.M. ; Snep, R.P.H. ; Slim, P.A. - \ 2011
    Ecological Modelling 222 (2011)17. - ISSN 0304-3800 - p. 3061 - 3070.
    density-dependent dispersal - common terns - population-dynamics - survival - evolution - habitat - models - gulls - size - performance
    Most seabirds live in large colonies. This fact signifies that there is an advantage in living and breeding together. Four explanations are put fore ward for this colonial behaviour, more birds have: (1) a reduced per capita predation of chicks in colonies, (2) a better anti-predator defence, (3) a more efficient foraging in temporally patchy environments and (4) sex ratios that are more likely to be close to one. These factors induce a strong Allee-type density-dependent relation, a positive relation between density and population growth rate at low density. Nevertheless, these Allee effects are generally ignored in seabird population studies. Therefore we study the consequences of introducing Allee-type density-dependent relations in a spatially explicit metapopulation model for the Common Tern (Sterna hirundo). Simulations show that Allee effects might be responsible for a 20-fold decline in the recolonization distances, causing patches and parts of metapopulations to effectively become more isolated. This leads to long recolonization times of empty breeding patches which consequently cause slower metapopulation expansion and recovery. Additionally, we show that the typical early warning signals, that show that a population is near its critical threshold induce by Allee effects, is less pronounced in colonies that are part of a metapopulation. Hence, we offer some simple equations to estimate critical densities and thresholds in a colony
    The banker plant method in biological control
    Huang, N. ; Enkegaard, A. ; Osborne, L.S. ; Ramakers, P.M.J. ; Messelink, G.J. ; Pijnakker, J. ; Murphy, G. - \ 2011
    Critical Reviews in Plant Sciences 30 (2011)3. - ISSN 0735-2689 - p. 259 - 278.
    aphid rhopalosiphum-padi - apparent competition - population-dynamics - encarsia-formosa - pest-management - trialeurodes-vaporariorum - aleyrodes-proletella - alternative host - gossypii glover - homoptera
    In the banker plant method, long-lasting rearing units for beneficials are created in the crop by distributing plants infested with herbivores or carrying other food items, such as pollen. The method has been widely investigated over many years and used to aid establishment, development and dispersal of beneficial organisms employed in biological control. In this review, we refine the definition of the banker plant method based on previous concepts and studies and offer the term “banker plant system” to describe the unit that is purposefully added to or established in a crop for control of pests in greenhouses or open field. The three basic elements of a banker plant system (banker plant, food source, beneficials) are discussed and illustrated with examples, and the diversity of banker plant systems (classified by target pest) used or investigated is documented. The benefits of using banker plant systems, such as low cost, increased freshness of beneficials, possibility for preventive control and for integration within IPM frameworks, make the method an interesting plant protection option with potential to enhance adoption of biological control in pest management programs.
    the role of mathematical modelling in understanding the epidemiology and control of sheep transmissible spongiform encephalopathies: a review
    Gubbins, S. ; Touzeau, S. ; Hagenaars, T.H.J. - \ 2010
    Veterinary Research 41 (2010)4. - ISSN 0928-4249 - p. 41:42 - 41:42.
    prion protein genotype - great-britain - classical scrapie - natural scrapie - british sheep - population-dynamics - norwegian sheep - bse infection - suffolk sheep - prp genotype
    To deal with the incompleteness of observations and disentangle the complexities of transmission much use has been made of mathematical modelling when investigating the epidemiology of sheep transmissible spongiform encephalopathies (TSE) and, in particular, scrapie. Importantly, these modelling approaches allow the incidence of clinical disease to be related to the underlying prevalence of infection, thereby overcoming one of the major difficulties when studying these diseases. Models have been used to investigate the epidemiology of scrapie within individual flocks and at a regional level; to assess the efficacy of different control strategies, especially selective breeding programmes based on prion protein (PrP) genotype; to interpret the results of scrapie surveillance; and to inform the design of surveillance programmes. Furthermore, mathematical modelling has played an important role when assessing the risk to human health posed by the possible presence of bovine spongiform encephalopathy in sheep. Here, we review the various approaches that have been taken when developing and analysing mathematical models for the epidemiology and control of sheep TSE and assess their impact on our understanding of these diseases. We also identify areas that require further work, discuss future challenges and identify data gaps.
    Food Quality in Producer-Grazer Models: A Generalized Analysis
    Stiefs, D. ; Voorn, G.A.K. van; Kooi, B.W. ; Feudel, U. ; Gross, T. - \ 2010
    American Naturalist 176 (2010)3. - ISSN 0003-0147 - p. 367 - 380.
    predator-prey interactions - population-dynamics - functional-response - stability - systems - stoichiometry - enrichment - connectance - coexistence - competition
    Stoichiometric constraints play a role in the dynamics of natural populations but are not explicitly considered in most mathematical models. Recent theoretical works suggest that these constraints can have a significant impact and should not be neglected. However, it is not yet resolved how stoichiometry should be integrated in population dynamical models, as different modeling approaches are found to yield qualitatively different results. Here we investigate a unifying framework that reveals the differences and commonalities between previously proposed models for producer-grazer systems. Our analysis reveals that stoichiometric constraints affect the dynamics mainly by increasing the intraspecific competition between producers and by introducing a variable biomass conversion efficiency. The intraspecific competition has a strongly stabilizing effect on the system, whereas the variable conversion efficiency resulting from a variable food quality is the main determinant for the nature of the instability once destabilization occurs. Only if the food quality is high can an oscillatory instability, as in the classical paradox of enrichment, occur. While the generalized model reveals that the generic insights remain valid in a large class of models, we show that other details such as the specific sequence of bifurcations encountered in enrichment scenarios can depend sensitively on assumptions made in modeling stoichiometric constraints.
    Spatial distribution of lion kills determined by the water dependency of prey species
    Boer, W.F. de; Vis, M.J.P. ; Knegt, H.J. de; Rowles, C. ; Kohi, E. ; Langevelde, F. van; Peel, M.J.S. ; Pretorius, Y. ; Skidmore, A.K. ; Slotow, R. ; Wieren, S.E. van; Prins, H.H.T. - \ 2010
    Journal of Mammalogy 91 (2010)5. - ISSN 0022-2372 - p. 1280 - 1286.
    kruger-national-park - panthera-leo - african herbivores - habitat selection - population-dynamics - hunting success - predation risk - abundance - serengeti - behavior
    Predation risk from lions (Panthera leo) has been linked to habitat characteristics and availability and traits of prey. We separated the effects of vegetation density and the presence of drinking water by analyzing locations of lion kills in relation to rivers with dense vegetation, which offer good lion stalking opportunities, and artificial water points with low vegetation density. The spatial distribution of lion kills was studied at the Klaserie Private Nature Reserve, South Africa. The distance between 215 lion kills and the nearest water source was analyzed using generalized linear models. Lions selected medium-sized prey species. Lion kills were closer to rivers and to artificial water points than expected by random distribution of the kills. Water that attracted prey, and not the vegetation density in riverine areas, increased predation risk, with kills of buffalo (Syncerus caffer), kudu (Tragelaphus strepsiceros), and wildebeest (Connochaetes taurinus) as water-dependent prey species. Traits of prey species, including feeding type (food habits), digestion type (ruminant or nonruminant), or body size, did not explain locations of lion kills, and no seasonal patterns in lion kills were apparent. We argue that the cascading impact of lions on local mammal assemblages is spatially heterogeneous
    Allometric scaling of resource acquisition by ruminants in dynamic and heterogeneous environments
    Kramer, K. ; Prins, H.H.T. - \ 2010
    Ecological Modelling 221 (2010). - ISSN 0304-3800 - p. 2555 - 2564.
    functional-response - large herbivores - mammalian herbivores - competitive interactions - population-dynamics - foraging behavior - grazing ruminants - body-size - model - ecology
    We present a mechanistic formulation of the intake response of ruminants to vegetation biomass based solely on physiological and morphological parameters that scale allometrically with the animal's body mass. The model is applied to describe herbivore–vegetation interactions in dynamic and heterogeneous landscapes with low quality but abundant “tall grass” and high quality but sparsely available “short grass”, under two conditions: “uncoupled” (such that the effect of food intake on vegetation biomass can be neglected), or “coupled” (such that the vegetation biomass is determined by herbivore feeding). The results show that under uncoupled conditions, the minimum acceptance (proportion of vegetation consumed by the herbivore) at which the herbivore can leave its current patch without reducing its intake rate is when it has depleted the current patch by the energetic cost required to travel to another patch. The maximum acceptance at which the herbivore should leave its patch is when it has depleted the current patch by the cumulative energetic cost of traveling, handling, cropping, and digesting. Under coupled conditions, the optimal acceptance equals half the relative growth rate of the vegetation. Analytical solutions are obtained for equilibrium values for utilization of the vegetation, and for the densities of vegetation and ruminants, expressed in physiological and morphological herbivore parameters.
    Optimal weed management in crop rotations: incorporating economics is crucial
    Berg, F. van den; Gilligan, C.A. ; Lemmen-Gerdessen, J.C. van; Gregoire, L.A.H. ; Bosch, F. van den - \ 2010
    Weed Research 50 (2010)5. - ISSN 0043-1737 - p. 413 - 424.
    population-dynamics - bioeconomic model - yield loss - wild oats - system - seeds - interference - herbicide - density - soil
    Although the effects of crop rotation sequence and length on weed population dynamics have been studied, it is not clear whether or not the best strategy, from a weed population dynamics point of view, is also the economic optimal strategy. It is also not clear which biological and economic parameters are most important in determining this optimal strategy. We use a density-dependent periodic matrix model, integrated with an economic model, to study the effect of rotation length and weed control on the average annual net profit (ANP). The system of the weed Persicaria maculosa in carrots (crop A) and spring wheat (crop B) is used as an example case study. The bio-economic model shows that income is roughly constant with rotation length, apart from the shortest rotation sequence. These results are in agreement with a previous model study, which was restricted to biological dynamics. However, where the purely biological model suggests that weeding effort should be focussed on spring wheat years in the rotation, our bio-economic model shows that this is not a viable economic strategy. In fact, the mean ANP over a rotation is mainly determined by the ANP in carrot years (where the gross margin is high) and depends on the balance between the increase in seed population density in carrot years and its decrease in wheat years, in combination with weeding costs. The model can easily be extended to incorporate other damaging organisms, making the model broadly suitable for analysing a range of weed management strategies from an economic perspective.
    Estimating total mortality and asympotic length of Crangon crangon between 1955 and 2006
    Hufnagl, M. ; Temming, A. ; Siegel, V. ; Tulp, I.Y.M. ; Bolle, L.J. - \ 2010
    ICES Journal of Marine Science 67 (2010)5. - ISSN 1054-3139 - p. 875 - 884.
    wadden sea - north-sea - population-dynamics - common shrimp - bristol channel - abundance - atlantic - l. - climate - estuary
    Total mortality (Z, year–1) of southern North Sea brown shrimp (Crangon crangon) was determined as Z = K, based on the von Bertalanffy length–growth constant (K, year–1) and derived from length-based methods. Mortality estimates were based on length frequency distributions obtained from four long-term dataseries (1955–2006): German Demersal Young Fish Survey, Dutch Demersal Fish Survey, and two German Bycatch series (Büsum and East Frisia). Four methods to estimate and L were evaluated. Highest total mortality (Z = 8 year–1) was estimated for the early 1990s, and the lowest (Z = 4 year–1) for the 1960s. Accounting for these differences, a median Z rather than mean values was calculated for the whole series, and the value ranged from 5.74 (Ssentongo and Larkin method), through 5.65 (Beverton and Holt method) and 5.64 (Jones and Zalinge method), to 5.35 (length-converted catch curves). Over the whole period, an increase in and a decrease in the proportion of shrimps >60 mm in the catch was observed, whereas asymptotic length L remained constant (at 79.3 mm total length)
    Plant-soil feedback of native and range expanding plant species is insensitive to temperature
    Grunsven, R.H.A. van; Veenendaal, E.M. ; Bezemer, T.M. ; Putten, W.H. van der - \ 2010
    Oecologia 162 (2010)4. - ISSN 0029-8549 - p. 1059 - 1069.
    climate-change - changing climate - environmental characteristics - population-dynamics - ammophila-arenaria - co2 enrichment - pathogens - community - world - biota
    Temperature change affects many aboveground and belowground ecosystem processes. Here we investigate the effect of a 5°C temperature increase on plant–soil feedback. We compare plant species from a temperate climate region with immigrant plants that originate from warmer regions and have recently shifted their range polewards. We tested whether the magnitude of plant–soil feedback is affected by ambient temperature and whether the effect of temperature differs between these groups of plant species. Six European/Eurasian plant species that recently colonized the Netherlands (non-natives), and six related species (natives) from the Netherlands were selected. Plant–soil feedback of these species was determined by comparing performance in conspecific and heterospecific soils. In order to test the effect of temperature on these plant–soil feedback interactions, the experiments were performed at two greenhouse temperatures of 20/15°C and 25/20°C, respectively. Inoculation with unconditioned soil had the same effect on natives and non-natives. However, the effect of conspecific conditioned soil was negative compared to heterospecific soil for natives, but was positive for non-natives. In both cases, plant–soil interactions were not affected by temperature. Therefore, we conclude that the temperature component of climate change does not affect the direction, or strength of plant–soil feedback, neither for native nor for non-native plant species. However, as the non-natives have a more positive soil feedback than natives, climate warming may introduce new plant species in temperate regions that have less soil-borne control of abundance
    Assessing non-chemical weeding strategies through mechanistic modelling of blackgrass (Alopecurus myosuroides Huds.) dynamics
    Colbach, N. ; Kurstjens, D.A.G. ; Munier-Jolain, N.M. ; Dalbiès, A. ; Doré, T. - \ 2010
    European Journal of Agronomy 32 (2010)3. - ISSN 1161-0301 - p. 205 - 218.
    crop-rotation - population-dynamics - seed characteristics - nitrogen balances - generic model - soil climate - systems - management - tillage - simulation
    Because of environmental and health safety issues, it is necessary to develop strategies that do not rely on herbicides to manage weeds. Introducing temporary grassland into annual crop rotations and mechanical weeding are the two main features that are frequently used in integrated and organic cropping systems for this purpose. To evaluate the contribution of these two factors in interaction with other cropping system components and environmental conditions, the present study updated an existing biophysical model (i.e. AlomySys) that quantifies the effects of cropping system on weed dynamics. Based on previous experiments, new sub-models were built to describe the effects on plant survival and growth reduction of mechanical weeding resulting from weed seedling uprooting and covering by soil, and those of grassland mowing resulting from tiller destruction. Additional modifications described the effect of the multi-year crop canopy of grassland on weed survival, growth, development and seed return to the soil. The improved model was used to evaluate the weed dynamics over 27 years in the conventional herbicide-based cropping system most frequently observed in farm surveys (i.e. oilseed rape/winter wheat/winter barley rotation with superficial tillage) and then to test prospective non-chemical scenarios. Preliminary simulations tested a large range of mechanical weeding and mowing strategies, varying operation frequencies, dates and, in the case of mechanical weeding, characteristics (i.e. tool, working depth, tractor speed). For mechanical weeding soon after sowing, harrowing was better than hoeing for controlling weed seed production. The later the operation, the more efficient the hoeing and the less efficient the harrowing. Tractor speed had little influence. Increasing tilling depth increased plant mortality but increased weed seed production because of additional seed germination triggering by the weeding tool. Decreasing the interrow width for hoeing was nefarious for weed control. The best combinations were triple hoeing in oilseed rape and sextuple harrowing in cereals. The best mowing strategy was mowing thrice, every 4–6 weeks, starting in mid-May. The best individual options were combined, simulated over 27 years and compared to the herbicide-based reference system. If herbicide applications were replaced solely by mechanical weeding, blackgrass infestation could not be satisfactorily controlled. If a three-year lucerne was introduced into the rotation, weed infestations were divided by ten. Replacing chisel by mouldboard ploughing before winter wheat reduced weed infestations at short, medium and long term to a level comparable to the herbicide-based reference system.
    Long-term effects of ungulate browsing on forest composition and structure
    Didion, M.P. ; Kupferschmid, A.D. ; Bugmann, H. - \ 2009
    Forest Ecology and Management 258 (2009)Suppl.1. - ISSN 0378-1127 - p. S44 - S55.
    white-tailed deer - mountain forests - european alps - gap model - roe deer - population-dynamics - species composition - protection forests - picea-abies - impact
    The impact of ungulate herbivores on tree regeneration and its possible consequences for long-term forest dynamics has raised concerns worldwide. In many countries, ungulate management aims at constant animal densities, whereas unmanaged ungulate populations tend to fluctuate over time. The ecosystem consequences of constant vs. varying ungulate densities are largely unknown, and the exact density that is acceptable from a forestry point of view is highly uncertain as well. We used the gap model ForClim v2.9.5 to examine the effects of three browsing-related phenomena: (a) temporal changes in animal densities and thus oscillations in browsing intensity; (b) changes in the importance of browsing as a limiting factor relative to other limitations for ingrowth; and (c) growth suppression by browsing and hence different ingrowth rates for slow- vs. fast-growing trees. Results showed that ungulate herbivory can induce profound compositional and structural changes in forest stands: (a) oscillations in the browsing intensity led to compositional shifts that were less severe than under the corresponding constant browsing intensity; (b) an increase in the importance of browsing relative to other environmental factors caused a decrease in the incidence of palatable species; and (c) growth suppression strongly affected the numbers and composition of small trees of all species. We conclude that browsing can cause a shift not only in the structure and composition of tree regeneration, but also of the upper canopy in the long term. Management can manipulate forest ecosystems through the control of animal densities, and our results suggest that alternative management strategies for ungulate populations may be worth considering so as to provide “windows of opportunity” for forest regeneration in time and/or space.
    CREAM: A European Project on Mechanistic Effect Models for Ecological Risk Assessment of Chemicals
    Grimm, V. ; Ashauer, R. ; Forbes, V. ; Hommen, U. ; Preuss, T.G. ; Schmidt, A.M. ; Brink, P.J. van den - \ 2009
    Environmental Science and Pollution Research 16 (2009)6. - ISSN 0944-1344 - p. 614 - 617.
    population-dynamics - pesticides - invertebrates - survival
    Plant–soil feedback induces shifts in biomass allocation in the invasive plant Chromolaena odorata
    Beest, M. te; Stevens, N. ; Olff, H. ; Putten, W.H. van der - \ 2009
    Journal of Ecology 97 (2009)6. - ISSN 0022-0477 - p. 1281 - 1290.
    increased competitive ability - solidago-gigantea asteraceae - borne pathogens - pyrrolizidine alkaloids - south-africa - phenotypic plasticity - microbial communities - population-dynamics - ammophila-arenaria - biological-control
    1. Soil communities and their interactions with plants may play a major role in determining the success of invasive species. However, rigorous investigations of this idea using cross-continental comparisons, including native and invasive plant populations, are still scarce. 2. We investigated if interactions with the soil community affect the growth and biomass allocation of the (sub)tropical invasive shrub Chromolaena odorata. We performed a cross-continental comparison with both native and non-native-range soil and native and non-native-range plant populations in two glasshouse experiments. 3. Results are interpreted in the light of three prominent hypotheses that explain the dominance of invasive plants in the non-native range: the enemy release hypothesis, the evolution of increased competitive ability hypothesis and the accumulation of local pathogens hypothesis. 4. Our results show that C. odorata performed significantly better when grown in soil pre-cultured by a plant species other than C. odorata. Soil communities from the native and non-native ranges did not differ in their effect on C. odorata performance. However, soil origin had a significant effect on plant allocation responses. 5. Non-native C. odorata plants increased relative allocation to stem biomass and height growth when confronted with soil communities from the non-native range. This is a plastic response that may allow species to be more successful when competing for light. This response differed between native and non-native-range populations, suggesting that selection may have taken place during the process of invasion. Whether this plastic response to soil organisms will indeed select for increased competitive ability needs further study. 6. The native grass Panicum maximum did not perform worse when grown in soil pre-cultured by C. odorata. Therefore, our results did not support the accumulation of local pathogens hypothesis. 7. Synthesis. Non-native C. odorata did not show release from soil-borne enemies compared to its native range. However, non-native plants responded to soil biota from the non-native range by enhanced allocation in stem biomass and height growth. This response can affect the competitive balance between native and invasive species. The evolutionary potential of this soil biota-induced change in plant biomass allocation needs further study
    Continuous growth of the giant grass Zizaniopsis bonariensis in subtropical wetlands
    Finkler Ferreira, T. ; Nes, E.H. van; Motta Marques, D. da - \ 2009
    Freshwater Biology 54 (2009)2. - ISSN 0046-5070 - p. 321 - 330.
    aboveground primary production - typha-latifolia - emergent macrophytes - population-dynamics - modeling approach - germination - establishment - ecosystems - strategies - patterns
    1. Zizaniopsis bonariensis (giant grass) is an emergent macrophyte species endemic to subtropical wetlands in Brazil, Argentina, Paraguay and Uruguay. In this study, we show the effects of its continuous clonal reproduction and its 'phalanx' growth strategy in the Taim Wetland (southern Brazil). 2. The continuous clonal growth of this 3-m high grass gave rise to the emergence of 11.7 new shoots m-2 per month and a high total above ground production (2870 g dry weight m-2 year-1). The biomass of the new shoots emerging every month formed a wave of growth, moderated by only weak seasonal variation. 3. We show its phalanx growth strategy by analysing the variations in population density and shoot height within a transect through the stand canopy. The inverse relation between density and height from the border to the interior indicates self-regulation of biomass. 4. The plants modified their environment, enhancing resistance to drought within the stand and thus facilitating their dominance. This positive feedback suggests that the dominance of the plant might constitute an alternative state in subtropical wetlands
    Thermophillic Sidestream Anaerobic Membrane Bioreactors: The Shear Rate Dilemma
    Jeison, D.A. ; Telkamp, P. ; Lier, J.B. van - \ 2009
    Water Environment Research 81 (2009)11. - ISSN 1061-4303 - p. 2372 - 2380.
    waste-water treatment - cross-flow microfiltration - population-dynamics - size distribution - cake formation - particle-size - filtration - performance - digestion - flux
    Anaerobic biomass retention under thermophilic conditions has proven difficult. Membrane filtration can be used as alternative way to achieve high sludge concentrations. This research studied the feasibility of anaerobic membrane bioreactors (AnMBRs) under thermophilic conditions. A sidestream MBR was operated at crossflow velocities up to 1.5 m/s. For comparison, a thermophilic upflow sludge blanket reactor also was operated. Results confirmed that biomass retention may limit the performance of sludge bed reactors during long-term operation. During MBR operation, cake formation was identified as the key factor limiting the applicable flux. Low levels of irreversible fouling were observed. Even though high shear can provide an increase in particle back-transport, exposure of the sludge to a high shear stress produced a reduction of particle size, affecting the attainable flux. The concept of "shear rate dilemma'' is introduced to describe this dual effect of shear during the operation of MBRs. Water Environ. Res., 81, 2372 (2009).
    Effects of large herbivores on murid rodents in a South African savanna
    Hagenah, N. ; Prins, H.H.T. ; Olff, H. - \ 2009
    Journal of Tropical Ecology 25 (2009). - ISSN 0266-4674 - p. 483 - 492.
    small mammals - vegetative cover - microhistological analysis - population-dynamics - livestock exclosure - communities - diet - heterogeneity - preferences - diversity
    Our study presents experimentally based results on how large herbivore species affect savanna vegetation and thus murid rodents in the Hluhluwe-iMfolozi Park in KwaZulu-Natal, South Africa. We permanently excluded groups of large herbivore guilds of various body sizes (ranging from white rhino to hares) from sixteen 40 x 40-m plots of vegetation by using different fence types. We determined grass species composition and vegetation height and collected capture-mark-recapture data on murid rodents. Nutrient concentrations of the dominant grass species and rodent diet compositions were analysed. We found that herbivore species of different body sizes had different effects on murid rodents. The exclusion of medium-sized herbivores, such as warthog, impala and nyala increased the abundance of high-quality grass species, especially Panicum maximum. However, the dominant rodent species Lemniscomys rosalia preferred the most abundant grass species, rather than high-quality grasses. The absence of large bulk feeders, such as zebra, buffalo and white rhino led to an increase in vegetation height. In response. tall vegetation promoted both rodent abundance and species diversity and altered rodent species composition. Ultimately, our results indicate that the greatest effect on murid rodents came from the reduction of vegetation cover by large bulk feeders, which likely increased rodent predation risk.
    Subfossil bog-pine horizons document climate and ecosystem changes during the Mid-Holocene
    Eckstein, J. ; Leuschner, H.H. ; Bauerochse, A. ; Sass-Klaassen, U. - \ 2009
    Dendrochronologia 27 (2009)2. - ISSN 1125-7865 - p. 129 - 146.
    swedish boreal forest - tree-ring chronology - scots pine - sylvestris l. - raised bogs - environmental-change - population-dynamics - growth - sweden - history
    Extended dendrochronological investigations were performed on subfossil pine entombed in peat layers of former raised bogs in Lower Saxony (NW Germany). The aim was to study of dynamics in bog development in response to local environmental conditions and regional changes in climate throughout the Holocene. To date, 1702 samples have been collected from 36 locations. Crossdating with the Lower Saxony Bog Oak Chronology (LSBOC) resulted in five absolutely dated pine chronologies covering large parts of the period from 5600 BC to 2200 BC. Radiocarbon dating of eight additional chronologies extends this time-span from 7000 BC to 1500 BC. By combining dendrochronology with information on stratigraphic position as well as stem and root morphology we found that major changes in site hydrology cause changes in growth pattern and population dynamics of subfossil pine whereas storm and fire were of minor importance. The fact that shifts in growth patterns and population dynamics occurred simultaneously in trees from different sites indicates regional climate changes as main drivers of pines forest development in peatland ecosystems
    Habitat heterogeneity as a driver of ungulate diversity and distribution patterns: interaction of body mass and digestive strategy
    Cromsigt, J.P.G.M. ; Prins, H.H.T. ; Olff, H. - \ 2009
    Diversity and Distributions 15 (2009)3. - ISSN 1366-9516 - p. 513 - 522.
    kruger-national-park - grazing lawns - herbivore assemblages - nutritional ecology - population-dynamics - african savannas - protected areas - south-africa - size - serengeti
    Aim Classic island biogeographical theory predicts that reserves have to be large to conserve high biodiversity. Recent literature, however, suggests that habitat heterogeneity can counterbalance the effect of small reserve size. For savanna ungulates, body mass is said to drive habitat selection and facilitate species coexistence, where large species use a higher proportion of the landscape than smaller species, because a wider food quality tolerance allows them to use a higher diversity of habitat types. In this case, high habitat heterogeneity would facilitate diverse assemblages of different-sized ungulates. Digestive physiology should further modify this relationship, because non-ruminants have a wider diet tolerance than ruminants. We tested this hypothesis with an empirical dataset on distribution and habitat preference of different-sized African grazers. Location Hluhluwe-iMfolozi Park, Republic of South Africa. Methods We recorded herbivore dung and habitat type on 24 line transects varying between 4 and 11 km with a total length of 190 km to determine habitat selection and landscape distribution of six grazer species, three ruminants and three non-ruminants. Results Larger ruminant grazers were more evenly distributed than smaller ruminants, had a more diverse use of habitats and used more low quality habitat. In contrast, non-ruminant grazers were more evenly distributed than similar-sized ruminants and body mass did not clearly influence diversity of habitat use and use of low quality habitat. Main conclusions We confirm that body mass influences diversity of habitat use of large herbivores but digestive strategy potentially modifies this relationship. Hence, habitat heterogeneity might facilitate herbivore diversity in savanna ecosystems and high heterogeneity might counterbalance the effects of fragmentation and declining reserve size. Concluding, processes that homogenize the landscape, such as fire (mis)management and artificial waterholes, might be as threatening to biodiversity as landscape fragmentation, especially for smaller ruminant herbivores
    Recruitment and attrition of associated plants under a shading crop canopy: Model selection and calibration
    Stilma, E.S.C. ; Keesman, K.J. ; Werf, W. van der - \ 2009
    Ecological Modelling 220 (2009)8. - ISSN 0304-3800 - p. 1113 - 1125.
    agri-environment schemes - population-dynamics - agricultural landscapes - light interception - arable weeds - biodiversity - germination - management - growth - yield
    Associated plant and animal diversity provides ecosystem services within crop production systems. The importance of the maintenance or restoration of diversity is therefore increasingly acknowledged. Here we study the population dynamics of associated annual plants (`weeds¿) during the growth of a crop in a season and introduce a minimal model to characterize the recruitment and attrition of the associated plants under the influence of shading by the crop. A mechanistically based, logistic, light interception model was parameterized with light interception measurements in two single crops (barley and rye) and in mixtures of these cereals with peas. Population dynamics data were collected for the annuals Papaver rhoeas, Centaurea cyanus, Chrysanthemum segetum, and Misopates orontium. A minimal population dynamics model was identified for each annual plant species, using system identification techniques as model selection and calibration. For three of the four species, a two-parameter model consisting of light-dependent recruitment in combination with a constant death rate, explained 75¿96% of the variation in plant densities over the season. Model fit for P. rhoeas improved when a germination delay of 200 °Cd after sowing was included, resulting in a three-parameter model. The developed models have a simple yet biologically meaningful structure and the values of the parameters give a useful summary of the population dynamics of an annual plant population under the influence of the dynamic leaf cover of a shading crop. Further development of these models can contribute to systems design for maintaining plant diversity in crop systems.
    Oviposition behaviour and egg distribution of the European corn borer, Ostrinia nubilalis, on maize, and its effect on host finding by Trichogramma egg parasitoids
    Suverkropp, B.P. ; Dutton, A. ; Bigler, F. ; Lenteren, J.C. van - \ 2008
    Bulletin of Insectology 61 (2008)2. - ISSN 1721-8861 - p. 303 - 312.
    sweet corn - field corn - population-dynamics - hbn lep - lepidoptera-pyralidae - spatial-distribution - biological-control - baden-wurttemberg - natural enemies - within-plant
    Oviposition behaviour and egg distribution of Ostrinia nubilalis is reviewed based on published information and new research. The position of egg masses of O. nubilalis on maize plants and leaves were sampled in the field. Most egg masses were found on the lower leaf side, on the middle part of the leaf or close to the stem, and close to the mid-rib. Direct observations of oviposition behaviour were made in laboratory and field cages. O. nubilalis moved very little on the plants and only 10 % of the females that landed on the plants oviposited. The number of actual ovipositions was quite low compared to the number of landings, with females walking only a few centimetres if at all. Shed scales of adult moths were not abundant near egg masses with only 37% of egg masses associated with scales and 45% with only a few scales. Many scales were found on other places of the plants. At the leaf and plant level, scales might serve as a useful host-cue to Trichogramma brassicae, an egg parasitoid of O. nubilalis. However, scales are not an indicator for the presence of egg masses in their immediate vicinity.
    Biological control of Trialeurodes vaporariorum by Encarsia formosa on tomato in unheated greenhouses in the high altitude tropics
    Vis, R.M.J. de; Lenteren, J.C. van - \ 2008
    Bulletin of Insectology 61 (2008)1. - ISSN 1721-8861 - p. 43 - 57.
    parasite-host relationship - commercial glasshouse - population-dynamics - aphelinidae - aleyrodidae - netherlands
    Biological control of Trialeurodes vaporariorum (Westwood) by Encarsia formosa Gahan was tested during three consecutive production cycles (16-28 weeks) on a beef tomato (Solanum lycopersicum L.) crop in a glasshouse and a plastic greenhouse on the Bogota Plateau in Colombia. During the course of this study over the period 1997-1999, the mean temperature was around 16 °C in the plastic greenhouse and around 17 °C in the glasshouse. E. formosa was introduced at a rate of 3 adults per m2 per week in the 1997 production cycle, and at a rate of 3 and 5 pupae per m2 per week in 1998 and 1999, respectively. In 1997, the adult whitefly population increased exponentially to a peak of 76 adults per plant in the plastic greenhouse, while the whitefly population in the glasshouse reached a peak of only 12 adults per plant. The percentage parasitism fluctuated between 42 and 82% in the glasshouse and between 28 and 47% in the plastic greenhouse. In 1998, the T. vaporariorum population could not be brought under control in both greenhouses and reached a peak of 80 and 53 T. vaporariorum adults per plant in the plastic greenhouse and the glasshouse, respectively. Parasitism fluctuated between 55 and 97% in the glasshouse and between 32 and 84% in the plastic greenhouse. In 1999, biological control was successful in both greenhouses. Most of the time, populations of T. vaporariorum were lower than 1.2 adults per plant and parasitism by E. formosa was 80% or higher. We suggest that the higher temperature is the main reason for better parasitism in the glasshouse when compared to the plastic greenhouse. The successful results of 1999 show that biological control is possible under the short day and low temperature conditions of greenhouses situated in the high altitude tropics such as the Bogota Plateau. Recommendations are given for the application of E. formosa based on the results of these experiments.
    Multiple species-specific controls of root-feeding nematodes in natural soils
    Piskiewicz, A.M. ; Duyts, H. ; Putten, W.H. van der - \ 2008
    Soil Biology and Biochemistry 40 (2008)11. - ISSN 0038-0717 - p. 2729 - 2735.
    plant-parasitic nematodes - grass ammophila-arenaria - biological-control - borne fungi - marram grass - ectoparasitic nematodes - endoparasitic nematodes - population-dynamics - coastal foredunes - fusarium wilts
    One of the major limitations to enhance sustainability of crop production systems is the inability to control root-feeding nematodes without using chemical biocides. In soils under wild vegetation, however, root-feeding nematodes affect plant performance and plant community composition varying from substantially to insignificantly. Previous studies in natural ecosystems have already shown that mutualistic symbionts, such as arbuscular mycorrhizal fungi and endophytes, may influence plant exposure to root-feeding nematodes. In order to learn more from natural systems, we examined nematode control in the root zone of a wild coastal foredune grass by microorganisms, other nematodes and microarthropods. We cultured all eight root-feeding nematode species that occur in the root zone of marram grass (Ammophila arenaria) in coastal foredunes of the Netherlands. Then, in an indoor growth experiment we exposed each nematode species to the potential natural antagonists collected from the same dune soil. Most of the eight dominant root-feeding nematode species could be controlled to some extent by more than one group of soil organisms added. The effectiveness of control varied among nematode species, which seemed to be controlled in a species-specific way. We conclude that in a natural soil the effectiveness of control by microorganisms, other nematodes or microarthropods varies among root-feeding nematode species. Most are controlled, at least to some extent, by soil microbes. However, some root-feeding nematode species are controlled only by microarthropods. Our results strongly suggest that sustainable agriculture will benefit from using a range of biological control mechanisms when controlling root-feeding nematodes, rather than relying on single control agents. Our suggestion also implies that conserving soil biodiversity is crucial in order to enhance the reliability of biological crop protection against soil-borne pests and diseases.
    Silviculture enhances the recovery of overexploited mahogany Swietenia macrophylla
    Verwer, C.C. ; Peña-Claros, M. ; Staak, D. van der; Ohlson-kiehn, K. ; Sterck, F.J. - \ 2008
    Journal of Applied Ecology 45 (2008)6. - ISSN 0021-8901 - p. 1770 - 1779.
    big-leaf mahogany - population-dynamics - seedling survival - tropical forest - rain-forest - growth - king - bolivia - trees - regeneration
    Big leaf mahogany Swietenia macrophylla is the most valuable timber species in the tropics but its future as a commercial timber species is at risk. This study evaluates whether recovery of overexploited mahogany populations is enhanced by actively managing the species and its surrounding forest. We assessed the effect of four different management interventions that varied in their intensities of harvesting and silvicultural treatments. We tested the hypothesis that intensive forest management stimulates population growth rates. Data were gathered over a 4-year period in the plots (326 ha) of the Long Term Silvicultural Research Program in Bolivia. Plants > 1·3 m tall were identified and monitored in the plots, while seedlings and saplings (<1·3 m tall) were recorded and measured around 58 adult mahogany trees. Population growth rate was simulated using population matrices based on observed vital rates. The application of silvicultural treatments only had an effect on seedling and sapling survival; survival being lowest in the unlogged forest and highest at intermediate levels of treatment application. Growth of larger trees tended to increase with management intensity, and was dependent on crown position and liana infestation. Removal of lianas and other competing trees had a positive effect on growth rates. Model simulations suggested that the recovery of overexploited mahogany population is enhanced by the application of intermediate levels of silvicultural treatments. Recovery is dependent on the retention of large seed trees (> 70 cm diameter at 1·3 m height) that produce large numbers of seedlings. Harvesting simulations indicate that mahogany populations can only be sustainably harvested by increasing the cutting cycle length, reducing harvesting intensity and by maintaining optimal growing conditions. Synthesis and applications. Mahogany is the most valuable timber species in the tropics, and its range has dramatically decreased mostly due to commercial harvesting. The results of simulation modelling based on field and experimental data suggest that overexploited populations are recovering and that sustainable harvesting will be possible in the future when cutting cycle length is increased, harvesting intensity is reduced and silvicultural treatments are applied regularly throughout the cutting cycle
    Polyandry and polygyny in an African rodent pest species, Mastomys natalensis
    Kennis, J. ; Sluydts, V. ; Leirs, H. ; Hooft, W.F. van - \ 2008
    Mammalia 72 (2008)3. - ISSN 0025-1461 - p. 150 - 160.
    squirrels sciurus-vulgaris - reproductive success - computer-program - mating systems - small mammals - population-dynamics - social-organization - parental genotypes - spacing behavior - southern-africa
    Males and females use different mating strategies and seldom have these strategies been studied on the field for cryptic rodent species. We studied the breeding strategies of both males and females of the sub-Sahara African rodent pest species, Mastomys natalensis, in the field using capture removal and capture-mark-recapture techniques combined with microsatellite analyses. In total, 36 litters (359 young) and 94 candidate fathers were genotyped. Multiple paternity (more than one male per litter) occurs frequently in all sampled grids (>47% of all litters). Paternity assignment success rates are relatively high (mean 69%). Males are polygynous, but this is less frequent than female polyandry. Large differences in male reproductive success exist with a large part of the male population without offspring in our sample. Larger males father significantly more offspring. Spatial analyses do not show a strict spatial organisation. Our data suggest male M. natalensis roam around to mate with as many females as possible, while females also mate with several males to produce litters fathered by several males. This species could be an interesting candidate for testing virally vectored immunocontraception as a pest management technique due to the promiscuous mating and high frequency of sexual contacts.
    The arms race between fishers
    Rijnsdorp, A.D. ; Poos, J.J. ; Quirijns, F.J. ; Hille Ris Lambers, R. ; Wilde, J.W. de; Heijer, W.M. den - \ 2008
    Journal of Sea Research 60 (2008)1-2. - ISSN 1385-1101 - p. 126 - 138.
    north-sea plaice - hake merluccius-bilinearis - maturation reaction norms - fishing vessels - mixed fisheries - fleet dynamics - behavioral inferences - population-dynamics - beam trawlers - catch
    An analysis of the changes in the Dutch demersal fishing fleet since the 1950s revealed that competitive interactions among vessels and gear types within the constraints imposed by biological, economic and fisheries management factors are the dominant processes governing the dynamics of fishing fleets. Double beam trawling, introduced in the early 1960s, proved a successful fishing method to catch deep burying flatfish, in particular sole. In less than 10 years, the otter trawl fleet was replaced by a highly specialised beam trawling fleet, despite an initial doubling of the loss rate of vessels due to stability problems. Engine power, size of the beam trawl, number of tickler chains and fishing speed rapidly increased and fishing activities expanded into previously lightly fished grounds and seasons. Following the ban on flatfish trawling within the 12 nautical mile zone for vessels of more than 300 hp in 1975 and with the restriction of engine power to 2000 hp in 1987, the beam trawl fleet bifurcated. Changes in the fleet capacity were related to the economic results and showed a cyclic pattern with a period of 6¿7 years. The arms race between fishers was fuelled by competitive interactions among fishers: while the catchability of the fleet more than doubled in the ten years following the introduction of the beam trawl, a decline in catchability was observed in reference beam trawlers that remained the same. Vessel performance was not only affected by the technological characteristics but also by the number and characteristics of competing vessels.
    Spatial and temporal patterns of carabid activity-density in cereals do not explain levels of predation on weed seeds
    Saska, P. ; Werf, W. van der; Vries, E. de; Westerman, P.R. - \ 2008
    Bulletin of Entomological Research 98 (2008)2. - ISSN 0007-4853 - p. 169 - 181.
    ground beetles coleoptera - crop-rotation systems - postdispersal predation - population-dynamics - fields - invertebrates - temperature - insects - tillage - food
    Seed predation is an important component of seed mortality of weeds in agro-ecosystems, but the agronomic use and management of this natural weed suppression is hampered by a lack of insight in the underlying ecological processes. In this paper, we investigate whether and how spatial and temporal variation in activity-density of granivorous ground beetles (Coleoptera: Carabidae) results in a corresponding pattern of seed predation. Activity-density of carabids was measured by using pitfall traps in two organic winter wheat fields from March to July 2004. Predation of seeds (Capsella bursa-pastoris, Lamium amplexicaule, Poa annua and Stellaria media) was assessed using seed cards at the same sites and times. As measured by pitfall traps, carabids were the dominant group of insects that had access to the seed cards. In the field, predation of the four different species of seed was in the order: C. bursa-pastoris>P. annua>S. media>L. amplexicaule; and this order of preference was confirmed in the laboratory using the dominant species of carabid. On average, seed predation was higher in the field interior compared to the edge, whereas catches of carabids were highest near the edge. Weeks with elevated seed predation did not concur with high activity-density of carabids. Thus, patterns of spatial and temporal variation in seed predation were not matched by similar patterns in the abundance of granivorous carabid beetles. The lack of correspondence is ascribed to effects of confounding factors, such as weather, the background density of seeds, the composition of the carabid community, and the phenology and physiological state of the beetles. Our results show that differences in seed loss among weed species may be predicted from laboratory trials on preference. However, predator activity-density, as measured in pitfall traps, is an insufficient predictor of seed predation over time and space within a field
    Biological control of thrips and whiteflies by a shared predator: Two pests are better than one
    Messelink, G.J. ; Maanen, B. ; Steenpaal, S.E.F. van; Janssen, A. - \ 2008
    Biological Control 44 (2008)3. - ISSN 1049-9644 - p. 372 - 379.
    mediated apparent competition - phytoseiid predators - population-dynamics - alternative food - bemisia-tabaci - control agents - prey - plants - consequences - communities
    We studied the capacity of one species of predator to control two major pests of greenhouse crops, Western flower thrips (Frankliniella occidentalis (Pergande)) and the greenhouse whitefly (Trialeurodes vaporariorum (Westwood)). In such a one-predator¿two-prey system, indirect interactions can occur between the two pest species, such as apparent competition and apparent mutualism. Whereas apparent competition is desired because it brings pest levels down, apparent mutualism is not, because it does the opposite. Because apparent competition and apparent mutualism occurs at different time scales, it is important to investigate the effects of a shared natural enemy on biological control on a time scale relevant for crop growth. We evaluated the control efficacy of the predatory mites Amblyseius swirskii (Athias-Henriot) and Euseius ovalis (Evans) in cucumber crops in greenhouse compartments with only thrips, only whiteflies or both herbivorous insects together. Each of the two predators controlled thrips, but A. swirskii reduced thrips densities the most. There was no effect of the presence of whiteflies on thrips densities. Whitefly control by each of the two predators in absence of thrips was not sufficient, yet better with E. ovalis. However, whitefly densities in presence of thrips were reduced dramatically, especially by A. swirskii. The densities of predators were up to 15 times higher in presence of both pests than in the single-pest treatments. Laboratory experiments with A. swirskii suggest that this is due to a higher juvenile survival and developmental rate on a mixed diet. Hence, better control may be achieved not only because of apparent competition, but also through a positive effect of mixed diets on predator population growth. This latter phenomenon deserves more attention in experimental and theoretical work on biological control and apparent competition.
    Soil food web structure during ecosystem development after land abandonment
    Holtkamp, R. ; Kardol, P. ; Wal, A. van der; Dekker, S.C. ; Putten, W.H. van der; Ruiter, P.C. de - \ 2008
    Applied Soil Ecology 39 (2008)1. - ISSN 0929-1393 - p. 23 - 34.
    bacterial biomass ratios - scots pine forest - nitrogen mineralization - organic-matter - agricultural systems - population-dynamics - community structure - functional-groups - fungal biomass - diversity
    The re-establishment of natural species rich heathlands on abandoned agricultural land is a common land use change in North-West Europe. However, it can take several decades to re-establish natural species rich heathland vegetation. The development rate has found to depend both on soil food web composition and on soil processes. We measured the soil food web composition in three ex-arable fields abandoned 2, 9 and 22 years ago and in a heathland. To characterize food structure, we defined four trophic levels and a root, fungal and bacterial energy channel. We hypothesized that with increasing time since abandonment, i.e. field age, (1) the basic resource level biomass, i.e. soil organic matter (SOM) and roots, will increase and thereby also that of biomasses at higher trophic levels, (2a) the root energy channel biomass will decrease, (2b) the fungal energy channel biomass will increase, and (2c) the bacterial energy channel biomass will not change. The results showed that biomasses at the basic resource level and at the first trophic level indeed increased with field age, but not the biomasses at higher trophic levels. It is not clear what the cause of the lack of increase in higher trophic levels was, possibly top-down or bottom-up forces played a role. The root energy channel biomass decreased and the fungal channel increased as hypothesized, but the bacterial channel biomass also increased with field age. The increase of the bacterial channel biomass contradicted the hypothesis, but agreed with the observed increase in SOM quantity and lack of decrease in SOM quality. On overall, results show that changes in belowground food webs lag behind changes of the aboveground vegetation. Such time lags may hamper secondary vegetation succession. Understanding those time lags may therefore help to develop management schemes improving land conversion processes
    A functional-structural model for growth of clonal bunchgrasses
    Tomlinson, K.W. ; Dominy, J.G. ; Hearne, J.W. ; O'Connor, T.G. - \ 2007
    Ecological Modelling 202 (2007)3-4. - ISSN 0304-3800 - p. 243 - 264.
    wheat triticum-aestivum - simulation-model - schizachyrium-scoparium - population-dynamics - organ interactions - tallgrass prairie - plant-responses - light-intensity - grass sward - root-system
    Interactions between structural architecture and resource allocation affect the ability of plants to utilise environmental resources. Architecture defines the structural layout and relationships of organs and other structural units at different hierarchical levels in plants. Resource allocation determines how competing structural units are awarded resources at different levels of hierarchy. Functional-structural plant models combine architecture and resource allocation as interacting components of plant growth and functioning. Existing functional-structural plant models concentrate on growth of unitary trees and therefore, lack sufficient structural definition to simulate growth of clonal plants. on the other hand, simulation models designed to consider clonal growth rarely attempt to simulate clonal architecture at a more detailed level than individual ramets. This paper introduces a functional-structural type model, TILLERTREE, which integrates the architectural growth of bunchgrasses with resource capture and allocation of nitrogen and carbohydrate. Resource allocation is implemented using a procedural algorithm based on object hierarchy and priority, and not mechanistically The model is used to illustrate that growth of bunchgrass clones is regulated by patterns of resource allocation between competing units at low levels of hierarchy, by considering the effect of resource rules controlling secondary tiller recruitment on clonal growth. Simulations are conducted using a chosen model C-4 bunchgrass species Themeda triandra
    Is plant biodiversity driven by decomposition processes? An emerging new theory on plant diversity
    Mazzoleni, S. ; Bonanomi, G. ; Giannino, F. ; Rietkerk, M. ; Dekker, S.C. ; Zucconi, F. - \ 2007
    Community Ecology 8 (2007)1. - ISSN 1585-8553 - p. 103 - 109.
    old-field succession - seedling growth - soil feedback - population-dynamics - species richness - tropical forest - ecological significance - germination inhibition - litter decomposition - spatial-patterns
    Diversity of forest trees ranges from monospecific stands to the astonishing richness of tierra firma tropical forests. Such patterns are observed along gradients of latitude, altitude, soil fertility and rainfall. So far, the proposed coexisting mechanisms do not provide a comprehensive and unequivocal explanation of these patterns at the community level. We propose a new theory linking species diversity with organic matter cycle and negative plant-soil feedback induced by litter autotoxicity. This approach focuses on resource-waste rather than resource-only dynamics. High diversity does occur where litter decomposition is rapid and ecosystem nutrient cycles are closed. On the other hand, single species dominance is found where litter decomposition is slow and/or autotoxicity is removed from the nutrient cycle pathway. Unlike previous theoretical views, the one we present proves potentially capable of explaining differences in species diversity both along environmental gradients and within the tropics.
    Microbe-mediated plant-soil feedback causes historical contingency effects in plant community assembly
    Kardol, P. ; Cornips, N.J. ; Kempen, M.M.L. van; Bakx-Schotman, J.M.T. ; Putten, W.H. van der - \ 2007
    Ecological Monographs 77 (2007)2. - ISSN 0012-9615 - p. 147 - 162.
    16s ribosomal-rna - gradient gel-electrophoresis - food-web - population-dynamics - species coexistence - negative feedback - fungal pathogens - borne pathogens - diversity - succession
    Plant¿soil feedback affects performance and competitive ability of individual plants. However, the importance of plant¿soil feedback in historical contingency processes and plant community dynamics is largely unknown. In microcosms, we tested how six early-successional plant species of secondary succession on ex-arable land induced plant-specific changes in soil community composition. Following one growth cycle of conditioning the soil community, soil feedback effects were assessed as plant performance in soil of their own as compared to soil from a mixture of the other five early-successional species. Performance was tested in monocultures and in mixed communities with heterospecific competition from mid-successional species. The role of soil microorganisms was determined by isolating the microbial component from the soil community, re-inoculating microorganisms into sterilized substrate, and analyzing plant biomass responses of the early- and mid-successional species. Plant¿soil feedback responses of the early-successional species were negative and significantly increased when the plants were grown in a competitive environment with heterospecifics. In monocultures, three early-successional species experienced negative feedback in soil with a history of conspecifics, while all early-successional species experienced negative feedback when grown with interspecific competition. Interestingly, the nonnative forb Conyza canadensis showed the weakest soil feedback effect. Biomass production of the early-successional plant species was profoundly reduced by the microbial inocula, most strongly when exposed to inocula of conspecific origin. Molecular characterization of the fungal and bacterial rhizosphere communities revealed a relationship between plant biomass production and the composition of the dominant fungal species. Furthermore, our results show that, in early secondary succession, the early-successional plant species induce changes in the soil microbial community composition that cause historical contingency effects in dominance patterns of mid-succession plant communities. We conclude that feedback between early-successional plant species and soil microorganisms can play a crucial role in breaking dominance of early-successional plant communities. Moreover the influences on soil microorganism community composition influenced plant community dynamics in the mid-successional plant communities. These results shed new light on how feedback effects between plants and soil organisms in one successional stage result in a biotic legacy effect, which influences plant community processes in subsequent successional stages.
    Can overwintering versus diapausing strategy in Daphnia determine match-mismatch events in zooplankton-algae interactions?
    Senerpont Domis, L.N. de; Mooij, W.M. ; Hülsmann, S. ; Nes, E.H. van; Scheffer, M. - \ 2007
    Oecologia 150 (2007)4. - ISSN 0029-8549 - p. 682 - 698.
    north-atlantic oscillation - lake food webs - long-distance migrant - causes regime shifts - life-history traits - top-down control - climate-change - population-dynamics - seasonal dynamics - plankton dynamics
    Mismatches between predator and prey due to climate change have now been documented for a number of systems. Ultimately, a mismatch may have far-reaching consequences for ecosystem functioning as decoupling of trophic relationships results in trophic cascades. Here, we examine the potential for climate change induced mismatches between zooplankton and algae during spring succession, with a focus on Daphnia and its algal food. Whereas the development of an overwintering population of daphnids may parallel shifts in phytoplankton phenology due to climate warming, changes in the photoperiod¿temperature interaction may cause the emerging population of daphnids to hatch too late and mismatch their phytoplankton prey. A decoupling of the trophic relationship between the keystone herbivore Daphnia and its algal prey can result in the absence of a spring clear water phase. We extended an existing minimal model of seasonal dynamics of Daphnia and algae and varied the way the Daphnia population is started in spring, i.e., from free swimming individuals or from hatching resting eggs. Our model results show that temperature affects the timing of peak abundance in Daphnia and algae, and subsequently the timing of the clear water phase. When a population is started from a small inoculum of hatching resting eggs, extreme climate warming (+6°C) results in a decoupling of trophic relationships and the clear water phase fails to occur. In the other scenarios, the trophic relationships between Daphnia and its algal food source remain intact. Analysis of 36 temperate lakes showed that shallow lakes have a higher potential for climate induced match¿mismatches, as the probability of active overwintering daphnids decreases with lake depth. Future research should point out whether lake depth is a direct causal factor in determining the presence of active overwintering daphnids or merely indicative for underlying causal factors such as fish predation and macrophyte cover.
    Kauri trees (Agathis australis) affect nutrient, water and light availability for their seedlings
    Verkaik, E. ; Braakhekke, W.G. - \ 2007
    New Zealand Journal of Ecology 31 (2007)1. - ISSN 0110-6465 - p. 39 - 46.
    don lindl kauri - new-zealand - population-dynamics - soil interactions - forest remnants - litter - growth - decomposition - biology - shade
    Plants can change the soil that they grow on, for example by producing litter. If litter characteristics are such that their effect on the soil increases a plant's fitness, a positive feedback can develop between the plant and the soil. Several studies indicate that New Zealand kauri trees (Agathis australis) lower the availability of nutrients in the soil beneath their crown. Low nutrient availability would be positive for the survival of kauri seedlings as they are known to use nutrients more efficiently than angiosperm species. We tested the hypotheses that nutrient availability is lower and light availability is higher beneath kauri trees than beneath the surrounding angiosperm vegetation. We determined the availability of nutrients (using leaf nutrient concentrations as a proxy), soil moisture, and light in both situations. As a reference we did the same measurements in tea tree vegetation (Leptospermum scoparium and Kunzea ericoides) where kauri seedlings were abundant. The availability of nitrogen, phosphorus and calcium was lower under kauri than in the surrounding vegetation. Further, in a dry period the availability of water in the organic layer surrounding the kauri trunk was lower than in the mineral soil further away from the kauri trunk. We suggest that periodic drought explains why the density of kauri seedlings under mature kauri trees is less than in tea tree vegetation. Kauri seedlings are more tolerant of drought and low nutrient availability than other tree seedlings and we conclude that the conditions under mature kauri give kauri seedlings an advantage over seedlings of other tree species. The low nutrient availability under mature kauri trees supports the idea of a positive soil¿plant feedback driven by poor decomposability of kauri litter.
    Site conditions affect seedling distribution below and outside the crown of kauri trees (Agathis australis)
    Verkaik, E. ; Gardner, R.O. ; Braakhekke, W.G. - \ 2007
    New Zealand Journal of Ecology 31 (2007)1. - ISSN 0110-6465 - p. 13 - 21.
    tanekaha phyllocladus-trichomanoides - don lindl kauri - new-zealand - soil interactions - population-dynamics - forest - growth - litterfall - damage
    It has been suggested that plants can change soil characteristics via their litter to favour their own species. The New Zealand kauri tree (Agathis australis) presents an interesting case for studying such a positive feedback between plant and soil because it has a huge impact upon the soil. We hypothesised that, under mature kauri trees, compared with sites outside the projection of the crown, seedlings of angiosperm trees are relatively rare, while kauri seedlings are relatively common, due to the poor soil conditions and the higher light intensity. We counted seedlings under and outside the crowns of kauri trees and correlated the presence of these seedlings to measured site conditions. The results confirm the hypotheses and indicate that the establishment of kauri seedlings is favoured by the open canopy and high light intensities below kauri. The low nutrient availability under kauri appears to be unfavourable for the survival of angiosperm seedlings but not for the survival of kauri seedlings. Since the lower nitrogen availability under kauri is due to sequestration of nitrogen in the organic layer under kauri, a positive feedback between kauri and the soil is likely.
    Soil microorganisms control plant ectoparasitic nematodes in natural coastal foredunes
    Piskiewicz, A.M. ; Duyts, H. ; Berg, M.P. ; Costa, S.R. ; Putten, W.H. van der - \ 2007
    Oecologia 152 (2007)3. - ISSN 0029-8549 - p. 505 - 514.
    root-feeding caterpillars - grass ammophila-arenaria - biological-control - parasitic nematodes - entomopathogenic nematodes - food-web - population-dynamics - mycorrhizal fungi - clonal grass - marram grass
    Belowground herbivores can exert important controls on the composition of natural plant communities. Until now, relatively few studies have investigated which factors may control the abundance of belowground herbivores. In Dutch coastal foredunes, the root-feeding nematode Tylenchorhynchus ventralis is capable of reducing the performance of the dominant grass Ammophila arenaria (Marram grass). However, field surveys show that populations of this nematode usually are controlled to nondamaging densities, but the control mechanism is unknown. In the present study, we first established that T. ventralis populations are top-down controlled by soil biota. Then, selective removal of soil fauna suggested that soil microorganisms play an important role in controlling T. ventralis. This result was confirmed by an experiment where selective inoculation of microarthropods, nematodes and microbes together with T. ventralis into sterilized dune soil resulted in nematode control when microbes were present. Adding nematodes had some effect, whereas microarthropods did not have a significant effect on T. ventralis. Our results have important implications for the appreciation of herbivore controls in natural soils. Soil food web models assume that herbivorous nematodes are controlled by predaceous invertebrates, whereas many biological control studies focus on managing nematode abundance by soil microorganisms. We propose that soil microorganisms play a more important role than do carnivorous soil invertebrates in the top-down control of herbivorous ectoparasitic nematodes in natural ecosystems. This is opposite to many studies on factors controlling root-feeding insects, which are supposed to be controlled by carnivorous invertebrates, parasitoids, or entomopathogenic nematodes. Our conclusion is that the ectoparasitic nematode T. ventralis is potentially able to limit productivity of the dune grass A. arenaria but that soil organisms, mostly microorganisms, usually prevent the development of growth-reducing population densities.
    Changes in the spatial distribution of North Sea plaice (Pleuronectes platessa) and implications for fisheries management
    Keeken, O.A. van; Hoppe, M. van; Grift, R.E. ; Rijnsdorp, A.D. - \ 2007
    Journal of Sea Research 57 (2007)2-3. - ISSN 1385-1101 - p. 187 - 197.
    wadden sea - juvenile flatfishes - predation risk - fish size - trawling disturbance - population-dynamics - temperature - growth - behavior - impacts
    To protect the main nursery area of plaice, an area called the `Plaice Box¿ was closed to trawl fisheries with large vessels in 1989, with the expectation that recruitment, yield and spawning stock biomass would increase. However, since then the plaice population has declined and the rate of discarding outside the Plaice Box has increased, suggesting an offshore shift in spatial distribution of juvenile plaice. Using research vessel survey data collected since 1970, the change in distribution of juvenile age groups was analysed in relation to the distance to the coast. Further, a comparison of the distribution of different length classes of plaice between three historic periods was made (1902¿1909; 1983¿1987; 1999¿2003). A shift towards deeper water of larger-sized plaice (20¿39 cm) is apparent already before the 1980s and may be related to the decrease in the number of competitors or predators. An offshore shift in the distribution of young plaice occurred in the 1990s most likely in response to higher water temperatures that may have exceeded the maximum tolerance range or increased the food requirements above the available food resources. A decrease in competition with larger plaice offshore, possibly in combination with increased inshore predation by cormorants and seals, may also have played a role. The offshore shift in distribution has reduced the effectiveness of the Plaice Box as a technical measure to protect the under-sized plaice from discarding, since an increased proportion of the population of undersized plaice is moving to the more heavily exploited offshore areas.
    Assessing the intensity of temperate European agriculture at the landscape scale
    Herzog, F. ; Steiner, B. ; Bailey, D. ; Baudry, J. ; Billeter, R. ; Bukacek, R. ; Blust, G. de; Cock, R. de; Dirksen, J. ; Dormann, C. ; DeFilippi, R. ; Frossard, E. ; Liira, J. ; Schmidt, T. ; Stockli, R. ; Thenail, C. ; Wingerden, W.K.R.E. van; Bugter, R.J.F. - \ 2006
    European Journal of Agronomy 24 (2006)2. - ISSN 1161-0301 - p. 165 - 181.
    land-use intensity - population-dynamics - southern england - natural enemies - farming systems - soil fertility - use efficiency - resource use - intensification - diversity
    The intensity of agricultural production was assessed in 25 landscape test sites across temperate Europe using a standardised farmer questionnaire. The intensity indicators, nitrogen input (to arable crops and to permanent grassland), density of livestock units and number of pesticide applications (herbicides, insecticides, fungicides and retardants), were recorded and integrated into an overall intensity index. All three components were needed to appropriately characterise the intensity of agricultural management. Four hypotheses were tested. (i) A low diversity of crops is related to higher intensity. The contrary was observed, namely because diverse crop rotations contained a higher share of crops which are more demanding in terms of nitrogen and of plant protection. (ii) Intensity decreases when there is more permanent grassland. This was confirmed by our study. (iii) Large farms are managed more intensively. There was no relation between farm size and intensity. (iv) Large fields are managed more intensively. There was a tendency towards higher nitrogen input and livestock density in landscapes with larger fields but only a few of the results were statistically significant. The aggregated overall intensity index was of limited usefulness mainly because of limitations in interpretability.
    Interplay between Senecio jacobaea and plant, soil, and aboveground insect community composition
    Bezemer, T.M. ; Harvey, J.A. ; Kowalchuk, G.A. ; Korpershoek, H. ; Putten, W.H. van der - \ 2006
    Ecology 87 (2006)8. - ISSN 0012-9658 - p. 2002 - 2013.
    population-dynamics - biotic resistance - pyrrolizidine alkaloids - ammophila-arenaria - species richness - cinnabar moth - diversity - invasion - grassland - biodiversity
    To elucidate the factors that affect the performance of plants in their natural environment, it is essential to study interactions with other neighboring plants, as well as with above- and belowground higher trophic organisms. We used a long-term field experiment to study how local plant community diversity influenced colonization by the biennial composite Senecio jacobaea in its native range in The Netherlands in Europe. We tested the effect of sowing later-succession plant species (0, 4, or 15 species) on plant succession and S. jacobaea performance. Over a period of eight years, the percent cover of S. jacobaea was relatively low in communities sown with 15 or 4 later-succession plant species compared to plots that were not sown, but that were colonized naturally. However, after four years of high abundance, the density of S. jacobaea in unsown plots started to decline, and the size of the individual plants was smaller than in the plots sown with 15 or 4 plant species. In the unsown plots, densities of aboveground leaf-mining, flower-feeding, and stem-boring insects on S. jacobaea plants were lower than on plants in sown plots, and there was a strong positive relationship between plant size and levels of herbivory. In a greenhouse experiment, we grew S. jacobaea in sterilized soil inoculated with soil from the different sowing treatments of the field experiment. Biomass production was lower when S. jacobaea test plants were grown in soil from the unsown plots than in soil from the sown plots (4 or 15 species). Molecular analysis of the fungal and bacterial communities revealed that the composition of fungal communities in unsown plots differed significantly from those in sown plots, suggesting that soil fungi could have been involved in the relative growth reduction of S. jacobaea in the greenhouse bioassay. Our results show that, in its native habitat, the abundance of S. jacobaea depends on the initial composition of the plant community and that, on a scale of almost a decade, its interactions with plant and soil communities and aboveground invertebrates may influence the dynamics of this colonizing species.
    Bottlenecks and Spatiotemporal variation in the sexual reproduction pathway of perennial meadow plants.
    Jongejans, E. ; Soons, M.B. ; Kroon, H. de - \ 2006
    Basic and Applied Ecology 7 (2006)1. - ISSN 1439-1791 - p. 71 - 81.
    dispersal seed predation - microsite limitation - population-dynamics - solidago-altissima - grassland plants - recruitment - wind - establishment - germination - colonization
    Sexual reproduction is important for the growth of populations and the maintenance of genetic diversity. Several steps are involved in the sexual reproduction pathway of plants: the production of flowers, the production of seeds and the establishment of seedlings from seeds. In this paper we quantify the relative importance and spatiotemporal variability of these different steps for four grassland perennials: Centaurea jacea, Cirsium dissectum, Hypochaeris radicata and Succisa pratensis. We compared undisturbed meadows with meadows where the top soil layer had been removed as a restoration measure. Data on the number of flower heads per flowering rosette, the numbers of flowers and seeds per flower head, and the seedling establishment probabilities per seed were collected by field observations and experiments in several sites and years. Combination of these data shows that H. radicata and S. pratensis have higher recruitment rates (1.9 and 3.3 seedlings per year per flowering rosette, respectively) than the more clonal C. dissectum and C. jacea (0.027 and 0.23, respectively). Seedling establishment is the major bottleneck for successful sexual reproduction in all species. Large losses also occurred due to failing seed set in C. dissectum. Comparison of the coefficients of variation per step in space and time revealed that spatiotemporal variability was largest in seedling establishment, followed closely by flower head production and seed set
    Modelling the clonal growth of the rhizomatous macrophyte Potamogeton perfoliatus
    Wolfer, S.R. ; Nes, E.H. van; Straile, D. - \ 2006
    Ecological Modelling 192 (2006)1-2. - ISSN 0304-3800 - p. 67 - 82.
    division-of-labor - pectinatus l - simulation-model - aquatic plant - physiological integration - phragmites-australis - population-dynamics - posidonia-oceanica - cellular-automata - shallow lakes
    Macrophytes play a crucial role in the functioning of lake ecosystems. Until now most macrophyte models neglected the fact that the majority of macrophyte species expand clonally during the growing season. Inclusion of a detailed description of clonal growth in models can facilitate our understanding of space occupation and patch expansion and predict future macrophyte development. ¿CLOMO¿ is an individual-based model which includes a detailed, spatially explicit description of rhizome formation and clone expansion as well as a realistic description of photosynthesis including light limitation and temperature. The model also accounts for transfers of energy or resources between different parts of the clone (¿clonal integration¿). Although the clonal growth of macrophytes is complex and poorly known, the first model results for the macrophyte species Potamogeton perfoliatus were promising and compared well with the field data. The model can produce growth networks very similar to those found in the field. A Monte Carlo sensitivity analysis showed systematically which parameters have the largest effect on the architecture and expansion of the clones. The application of the model provided new insights into growth dynamics and patch development: (1) the model showed that a lack of branching will lead to the extinction of the clone after a certain number of years. This is due to the fact that the reproductive organs (turions) are formed at the end of a branch and even a small turion mortality will cause a reduction in surviving plant numbers; (2) the growth of rhizome axes relative to those in the previous year determines the patch density and patch expansion rate. Reversing rhizomes lead to compact patch growth whereas continuing rhizomes lead to loose aggregates.
    A review of the 1988 and 2002 phocine distemper virus epidemics in European harbour seals
    Härkönen, L. ; Dietz, R. ; Reijnders, P.J.H. ; Teilmann, J. ; Harding, K. ; Hall, A. ; Brasseur, S.M.J.M. ; Siebert, U. ; Goodman, S.J. ; Jepson, P.D. ; Rasmussen, T.D. ; Thompson, P. - \ 2006
    Diseases of Aquatic Organisms 68 (2006)2. - ISSN 0177-5103 - p. 115 - 130.
    morbillivirus infection - halichoerus-grypus - mass mortality - marine mammals - grey seals - organochlorine contaminants - population-dynamics - immune-responses - western atlantic - flame retardants
    We present new and revised data for the phocine distemper virus (PDV) epidemics that resulted in the deaths of more than 23 000 harbour seals Phoca vitulina in 1988 and 30 000 in 2002. On both occasions the epidemics started at the Danish island of Anholt in central Kattegat, and subsequently spread to adjacent colonies in a stepwise fashion. However, this pattern was not maintained throughout the epidemics and new centres of infection appeared far from infected populations on some occasions: in 1988 early positive cases were observed in the Irish Sea, and in 2002 the epidemic appeared in the Dutch Wadden Sea, 6 wk after the initiation of the outbreak at Anholt Island. Since the harbour seal is a rather sedentary species, such 'jumps' in the spread among colonies suggest that another vector species could have been involved. We discussed the role of sympatric species as disease vectors, and suggested that grey seal populations could act as reservoirs for PDV if infection rates in sympatric species are lower than in harbour seals. Alternatively, grey seals could act as subclinical infected carriers of the virus between Arctic and North Sea seal populations. Mixed colonies of grey and harbour seal colonies are found at all locations where the jumps occurred, It seems likely that grey seals, which show long-distance movements, contributed to the spread among regions. The harbour seal populations along the Norwegian coast and in the Baltic escaped both epidemics, which could be due either to genetic differences among harbour seal populations or to immunity. Catastrophic events such as repeated epidemics should be accounted for in future models and management strategies of wildlife populations.
    Flexible use of patch-leaving mechanisms in a parasitoid wasp
    Burger, J.M.S. ; Huang, Y. ; Hemerik, L. ; Lenteren, J.C. van; Vet, L.E.M. - \ 2006
    Journal of Insect Behavior 19 (2006)2. - ISSN 0892-7553 - p. 155 - 170.
    encarsia-formosa hymenoptera - vaporariorum homoptera-aleyrodidae - time allocation - trialeurodes-vaporariorum - host relationship - infochemical use - commercial glasshouse - population-dynamics - volatile emissions - venturia-canescens
    Classical optimal-foraging theory predicts that a parasitoid is less likely to leave a patch after a host encounter when the host distribution is aggregated, whereas a parasitoid is more likely to leave after a host encounter when the host distribution is regular. Field data on host distributions in the area of origin of the whitefly parasitoid Encarsia formosa showed that whiteflies aggregate at several spatial scales. However, infested leaves most likely contained a single host. This suggests that a host encounter is not enough to decide when to leave. We therefore tested the effect of host distribution and parasitoid experience on patch-leaving behavior. Each parasitoid was observed for several consecutive days in a three-dimensional arena with leaflets containing on average one host per leaflet in an either regular or aggregated host distribution. A proportional hazards model showed that a host encounter decreased the leaving tendency on a leaflet with one host when the time since the latest host encounter was short, but increased the leaving tendency when the time since the latest host encounter was long, independent of host distribution. We conclude that a parasitoid can switch from decreasing to increasing its tendency to leave a patch after a host encounter. We propose two hypotheses that may explain the evolution of such a switching mechanism.
    Accumulation of local pathogens: a new hypothesis to explain exotic plant invasions
    Eppinga, M.B. ; Rietkerk, M. ; Dekker, S.C. ; Ruiter, P.C. de; Putten, W.H. van der - \ 2006
    Oikos 114 (2006)1. - ISSN 0030-1299 - p. 168 - 176.
    soil-borne pathogens - enemy release hypothesis - grass ammophila-arenaria - below-ground biota - nematode communities - parasitic nematodes - population-dynamics - natural vegetation - l link - feedback
    Recent studies have concluded that release from native soil pathogens may explain invasion of exotic plant species. However, release from soil enemies does not explain all plant invasions. The invasion of Ammophila arenaria (marram grass or European beach grass) in California provides an illustrative example for which the enemy release hypothesis has been refuted. To explore the possible role of plant¿soil community interactions in this invasion, we developed a mathematical model. First, we analyzed the role of plant¿soil community interactions in the succession of A. arenaria in its native range (north-western Europe). Then, we used our model to explore for California how alternative plant¿soil community interactions may generate the same effect as if A. arenaria were released from soil enemies. This analysis was carried out by construction of a 'recovery plane' that discriminates between plant competition and plant¿soil community interactions. Our model shows that in California, the accumulation of local pathogens by A. arenaria could result in exclusion of native plant species. Moreover, this mechanism could trigger the rate and spatial pattern of invasive spread generally observed in nature. We propose that our 'accumulation of local pathogens' hypothesis could serve as an alternative explanation for the enemy release hypothesis to be considered in further experimental studies on invasive plant species
    Effects of host plant genotype and seedbank density on Striga reproduction
    Rodenburg, J. ; Bastiaans, L. ; Kropff, M.J. ; Ast, A. van - \ 2006
    Weed Research 46 (2006)3. - ISSN 0043-1737 - p. 251 - 263.
    population-dynamics - parasitic weed - hermonthica - sorghum - resistance - maize - infestation - expression - varieties - tolerance
    Prevention of seed input to the seedbank of Striga hermonthica-infested fields is an important objective of Striga management. In three consecutive years of field experimentation in Mali, Striga reproduction was studied for 10 sorghum genotypes at infestation levels ranging from 30 000 to 200 000 seeds m2. Host resistance was identified as an important determinant of Striga reproduction, with the most resistant genotypes (N13, IS9830 and SRN39) reducing Striga reproduction by 70¿93% compared with the most susceptible genotype (CK60-B). Seedbank density had a significant effect on Striga seed production. Higher seedbank density resulted in more Striga plants, which led to increased intra-specific competition and consequently a reduced level of reproduction per plant. For the most susceptible sorghum genotypes, density dependence also occurred in the earlier belowground stages. Striga reproduction continued beyond harvest. At the high infestation level just 8% of the total reproduction was realised after harvest, whereas at the low infestation level 39% was attained after harvest. Even though host-plant genotype plays a significant role in Striga reproduction, calculations indicated that only at very low infestation levels the use of the most resistant genotype was able to lower the Striga seedbank.
    The interplay between shifts in biomass allocation and costs of reproduction in four grassland perennials under simulated successional change
    Jongejans, E. ; Kroon, H. de; Berendse, F. - \ 2006
    Oecologia 147 (2006)2. - ISSN 0029-8549 - p. 369 - 378.
    resource-allocation - nutrient availability - sexual reproduction - population-dynamics - species-diversity - clonal plant - competition - vegetation - heathland - growth
    When perennial herbs face the risk of being outcompeted in the course of succession, they are hypothesized to either increase their biomass allocation to flowers and seeds or to invest more in vegetative growth. We tested these hypotheses in a 3-year garden experiment with four perennials (Hypochaeris radicata, Cirsium dissectum, Succisa pratensis and Centaurea jacea) by growing them in the midst of a tall tussock-forming grass (Molinia caerulea) that may successionally replace them in their natural habitat. In all species except for the short-lived H. radicata, costs of sexual reproduction were significant over the 3 years, since continuous bud removal enhanced total biomass or rosette number. To mimic succession we added nutrients, which resulted in a tripled grass biomass and higher death rates in the shorter-lived species. The simulated succession resulted also in a number of coupled growth responses in the survivors: enhanced plant size as well as elevated seed production. The latter was partly due to larger plant sizes, but mostly due to higher reproductive allocation, which in turn could be partly explained by lower relative somatic costs and by lower root¿shoot ratios in the high-nutrient plots. Our results suggest that perennial plants can increase both their persistence and their colonization ability by simultaneously increasing their vegetative size and reproductive allocation in response to enhanced competition and nutrient influxes. These responses can be very important for the survival of a species in a metapopulation context.
    Extreme climatic events shape arid and semiarid ecosystems
    Holmgren, M. ; Stapp, P. ; Dickman, C. ; Gracia, C. ; Graham, S. - \ 2006
    Frontiers in Ecology and the Environment 4 (2006)2. - ISSN 1540-9295 - p. 87 - 95.
    nino-southern oscillation - el-nino - long-term - population-dynamics - terrestrial ecosystems - functional-response - rodent populations - density-dependence - mammal assemblage - central australia
    Climatic changes associated with the El Nino Southern Oscillation (ENSO) can have a dramatic impact on terrestrial ecosystems worldwide, but especially on arid and semiarid systems, where productivity is strongly limited by precipitation. Nearly two decades of research, including both short-term experiments and long-term studies conducted on three continents, reveal that the initial, extraordinary increases in primary productivity percolate up through entire food webs, attenuating the relative importance of top-down control by predators, providing key resources that are stored to fuel future production, and altering disturbance regimes for months or years after ENSO conditions have passed. Moreover, the ecological changes associated with ENSO events have important implications for agroecosystems, ecosystem restoration, wildlife conservation, and the spread of disease. Here we present the main ideas and results of a recent symposium on the effects of ENSO in dry ecosystems, which was convened as part of the First Alexander von Humboldt International Conference on the El Nino Phenomenon and its Global Impact.
    Infochemicals structure marine, terrestrial and freshwater food webs: Implications for ecological informatics
    Vos, M. ; Vet, L.E.M. ; Wackers, F.L. ; Middelburg, J.J. ; Putten, W.H. van der; Mooij, W.M. ; Heip, C.H.R. ; Donk, E. van - \ 2006
    Ecological Informatics 1 (2006)1. - ISSN 1574-9541 - p. 23 - 32.
    antarctic procellariiform seabirds - dimethyl sulfide - inducible defenses - population-dynamics - tritrophic system - foraging success - cotesia-rubecula - parasitic wasps - plant volatiles - natural enemies
    Here we consider how information transfer shapes interactions in aquatic and terrestrial food webs. All organisms, whether they are dead or alive, release certain chemicals into their environment. These can be used as infochemicals by any other individual in the food web that has the biological machinery to sense and process such information. Such machinery has evolved in bacteria, plants and animals and has thus become an inextricable part of the mechanisms that underlie feeding relations in food webs. Organisms live in environments suffused with infochemicals and this information network can be tapped into by both predators and their prey. However, it also opens doors to confusion in the face of a bewildering abundance and complexity of information. Infochemical mixing, masking, crypsis and mimicry could cause such confusion, especially in species-rich communities. We provide a point of entry into this field of enquiry by identifying seminal papers and major reviews and by discussing research lines that might enhance our mechanistic understanding of interactions in food webs. We highlight empirical work on the ways in which individuals use infochemicals and discuss model results on how this mediates patterns of population dynamics. We consider implications for ecosystem management and indicate how classical models and novel approaches from ecological informatics may contribute to linking the levels of individuals, populations and communities and their interactions with abiotic structuring forces in ecosystems.
    Negative Plant-Soil Feedback and Positive Species Interaction in a Herbaceous Plant Community
    Bonanomi, G. ; Rietkerk, M. ; Dekker, S.C. ; Mazzoleni, S. - \ 2005
    Plant Ecology 181 (2005)2. - ISSN 1385-0237 - p. 269 - 278.
    population-dynamics - vegetation - grassland - facilitation - succession - tree - diversity - mortality - pathogens - patterns
    Increasing evidence shows that facilitative interaction and negative plant¿soil feedback are driving factors of plant population dynamics and community processes. We studied the intensity and the relative impact of negative feedback on clonal growth and seed germination of Scirpus holoschoenus, a `ring¿ forming sedge dominant in grazed grassland, and the consequences for species coexistence. The structure of aboveground tussocks was described. A Lithium tracer assessed belowground distribution of functional roots. Seed rain and seedling emergence were compared for different positions in relation to Scirpus tussocks. Soil bioassays were used to compare growth on soil taken from inside and outside Scirpus tussocks of four coexisting species (Mentha acquatica, Pulicaria dysenterica, Scirpus holoschoenus and Dittrichia viscosa). We also compared plant performance of dominant plant species inside and outside Scirpus tussocks in the field. The `ring¿ shaped tussocks of S. holoschoenus were generated by centrifugal rhizome development. Roots were functional and abundant under the tillers and extending outside the tussocks. The large roots mats that were present in the inner tussock zone were almost all dead. Seedling emergence and growth both showed a strong negative feedback of Scirpus in the inner tussock zone. Scirpus clonal development strongly reduced grass biomass. In the degenerated tussock zone, Pulicaria and Mentha mortality was lower, and biomass of individual plants and seed production were higher. This positive indirect interaction could be related to species-specific affinity to soil conditions generated by Scirpus, and interspecific competitive release in the degenerated tussock zone. We conclude that Scirpus negative feedback affects its seedling emergence and growth contributing to the development of the degenerated inner tussock zone. Moreover, this enhances species coexistence through facilitative interaction because the colonization of the inner tussock zone is highly species-specific.
    Persistence and coexistence of engineered baculoviruses
    Bonsall, M.B. ; O'Reilly, D.R. ; Cory, J.S. ; Hails, R.S. - \ 2005
    Theoretical Population Biology 67 (2005)4. - ISSN 0040-5809 - p. 217 - 230.
    insect-pathogen interactions - nuclear polyhedrosis-virus - udp-glucosyl transferase - recombinant baculovirus - trichoplusia-ni - egt gene - population-dynamics - spodoptera-exigua - gypsy-moth - host
    Baculoviruses, and in particular, the nucleopolyhedroviruses infect a wide range of arthropod hosts and have the potential to be used as biopesticides. However, one of the major drawbacks with these pathogens as biocontrol agents is that they have a slow response time. Alterations to the speed of kill and pathogen life history characteristics can influence the competitive outcome and persistence between wildtype and modified strains. Here, we explore, theoretically, how life-history modifications of pathogens can affect the epidemiology and ecology of strain coexistence. In particular, we show how under simple mass action disease transmission, life-history difference between strains are insufficient to allow coexistence. Additional heterogeneities in transmission are shown to be necessary to facilitate coexistence of wildtype and modified pathogen strains. We also illustrate how the patterns of infectivity of wildtype and modified strains can also affect long-term coexistence, and argue that appropriate assessment of genetic modifications must be presented in terms of relevant ecological theory.
    Habitat fragmentation reduces grassland connectivity for both short-distance and long-distance wind-dispersed forbs
    Soons, M.B. ; Messelink, J.H. ; Jongejans, E. ; Heil, G.W. - \ 2005
    Journal of Ecology 93 (2005)6. - ISSN 0022-0477 - p. 1214 - 1225.
    scale spatial dynamics - seed dispersal - landscape connectivity - population-dynamics - perennial herbs - roe deer - plants - performance - size - colonization
    1 Although habitat loss and fragmentation are assumed to threaten the regional survival of plant species, their effects on regional species dynamics via seed dispersal and colonization have rarely been quantified. 2 We assessed the impact of habitat loss and fragmentation on the connectivity, and hence regional survival, of wind-dispersed plant species of nutrient-poor semi-natural grasslands. We did this using a new approach to relate quantified habitat loss and fragmentation to quantified colonization capacity. 3 We quantified loss and fragmentation during the 20th century of moist, nutrient-poor semi-natural grasslands in study areas in the Netherlands, as well as their current distribution. After testing how well the habitat distribution matches species distributions of two wind-dispersed grassland forbs (Cirsium dissectum, representative of species with long-distance wind dispersal, and Succisa pratensis, representative of species with short-distance wind dispersal), we combined the habitat distribution data with simulated seed dispersal kernels in order to quantify the impact on connectivity. 4 Habitat loss and fragmentation has dramatically reduced both the area (by 99.8%) and the connectivity of the grasslands. The remaining grasslands are practically isolated for seeds dispersed by wind, even for species with high wind dispersal ability (for which, interestingly, connectivity by wind dispersal decreased most). Linear landscape elements hardly contribute to connectivity by wind dispersal. Regional survival of the studied species has become completely dependent on the survival of a few large populations in nature reserves. Other remaining populations are decreasing in number and size and have low colonization capacity. 5 Habitat loss and fragmentation have drastically changed the regional species dynamics of wind-dispersed plant species, indicating that it is of utmost importance to preserve remaining populations in nature reserves and that the probability of colonization of new or restored sites is very low, unless the sites are adjacent to occupied sites or dispersal is artificially assisted.
    A strategy to improve the contribution of complex simulation models to ecological theory
    Nes, E.H. van; Scheffer, M. - \ 2005
    Ecological Modelling 185 (2005)2-4. - ISSN 0304-3800 - p. 153 - 164.
    individual-based model - multiple stable states - oriented simulation - population-dynamics - shallow lakes - eutrophication - communities - macrophytes - competition - validation
    Large models are commonly used for simulations of past results or future scenario's of ecosystems. However, such models have been criticized, mainly because the causes of their results are hard to understand. Simple models have contributed more to the development of ecological theory. However, simple models usually neglect important aspects such as spatial heterogeneity and individual variability, and may focus too much on one of several possible causes of a phenomenon. In this paper, we present a strategy that we have found useful for improving our understanding of the way in which complex models generate their results. The strategy consists of three phases. The first phase is a thorough analysis of the model behavior with respect to a selected set of parameters ('scrutinizing'). Secondly, similar analyses are done with several simplified versions of the model ('simplifying'). In this step, relationships between state variables or species that may potentially cause incomprehensible behavior are replaced by fixed values or highly simplified relations. The last step is to explain the differences between the full and the simplified versions and to discuss the results in the light of the existing ecological theory ('synthesizing'). We argue that this way of combining analyses of simple and more elaborate models is a powerful way to gain understanding of complex systems.
    The influence of life history dynamics and environment on the determination of year class strength in North Sea herring (Clupea harengus L.)
    Nash, R.D.M. ; Dickey-Collas, M. - \ 2005
    Fisheries Oceanography 14 (2005)4. - ISSN 1054-6006 - p. 279 - 291.
    cod recruitment models - atlantic oscillation - theragra-chalcogramma - population-dynamics - walleye pollock - spawning stock - downs stock - arctic cod - egg weight - growth
    The inter-annual variability in year class strength (1976-2000) of North Sea herring (Clupea harengus) was investigated using Paulik diagrams based on survey data and Virtual Population Analysis. The herring life cycle was split into five stages: spawning stock biomass (SSB), egg production, larvae, fish with 0 winter rings on the otolith (0-wr), 1-wr and 2-wr. Surveys were used as indices and Paulik analysis revealed relationships between stages. In 80% of the years, year class strength reflected SSB. Poorer than expected year classes were determined during the larva to 0-wr phase, whilst stronger than expected year classes were apparently determined during the 0-wr to 1-wr stage. There was no clear relationship between survival of young stages of herring and the abundance of Calanus finmarchicus but the year class strength of 0-wr and 1-wr had a negative relationship to bottom water temperature. Lower sea water temperatures in the North Sea are associated with higher Calanus abundance. The analysis shows that the strength of aberrant year classes of North Sea herring is determined between the pelagic larval and the juvenile stages
    Scale-dependent feedback and regular spatial patterns in young mussel beds
    Koppel, J. van de; Rietkerk, M. ; Dankers, N.M.J.A. ; Herman, P.M.J. - \ 2005
    American Naturalist 165 (2005)3. - ISSN 0003-0147 - p. E66 - E77.
    self-organized criticality - benthic boundary-layer - mytilus-edulis l. - population-dynamics - semiarid vegetation - local interactions - differential flow - spectral-analysis - arid ecosystems - patch dynamics
    In the past decade, theoretical ecologists have emphasized that local interactions between predators and prey may invoke emergent spatial patterning at larger spatial scales. However, empirical evidence for the occurrence of emergent spatial patterning is scarce, which questions the relevance of the proposed mechanisms to ecological theory. We report on regular spatial patterns in young mussel beds on soft sediments in the Wadden Sea. We propose that scale-dependent feedback, resulting from short-range facilitation by mutual protection from waves and currents and long-range competition for algae, induces spatial self-organization, thereby providing a possible explanation for the observed patterning. The emergent self-organization affects the functioning of mussel bed ecosystems by enhancing productivity and resilience against disturbance. Moreover, self-organization allows mussels to persist at algal concentrations that would not permit survival of mussels in a homogeneous bed. Our results emphasize the importance of self-organization in affecting the emergent properties of natural systems at larger spatial scales.
    Competition between domestic livestock and wild bharal Pseudois nayaur in the Indian Trans-Himalaya
    Mishra, C. ; Wieren, S.E. van; Ketner, P. ; Heitkönig, I.M.A. ; Prins, H.H.T. - \ 2004
    Journal of Applied Ecology 41 (2004)2. - ISSN 0021-8901 - p. 344 - 354.
    population-dynamics - large herbivores - overlap
    1. The issue of competition between livestock and wild herbivores has remained contentious. We studied the diets and population structures of the mountain ungulate bharal Pseudois nayaur and seven species of livestock to evaluate whether or not they compete for forage. The study was conducted in the high altitude Spiti Valley, Indian Trans-Himalaya. 2. We compared resource (forage) availability and bharal population structures between rangelands differing in livestock density. Forage availability was estimated by clipping the standing graminoid biomass in sample plots. Livestock and bharal population structures were quantified through annual censuses. Seasonal diets of livestock were studied by direct observations, while those of bharal were quantified through feeding signs on vegetation. 3. We found that livestock grazing causes a significant reduction in the standing crop of forage. Graminoid availability per unit livestock biomass was three times greater in a moderately grazed rangeland compared with an intensively grazed one. 4. There was considerable diet overlap among the herbivore species. In summer, bharal, yak Bos grunniens, horse Equus caballus, cow Bos indicus, and dzomo (yak-cow hybrids) fed predominantly on graminoids, while donkey E. asinus, sheep Ovis aries, and goat Capra hircus, consumed both graminoids and herbs. The summer diet of bharal was a subset of the diets of three livestock species. In winter, depleted graminoid availability caused bharal, yak and horse to consume relatively more herbs, while the remaining livestock species fed predominantly on graminoids. Diet overlap was less in winter but, in both seasons, all important forage species in the bharal diet were consumed in substantial amounts by one or more species of livestock. 5. Comparison of the population structures of bharal between two rangelands differing in livestock density by c. 30% yielded evidence of resource competition. In the intensively grazed rangeland, bharal density was 63% lower, and bharal population showed poorer performance (lower young : adult female ratios). 6. Synthesis and applications. High diet overlap between livestock and bharal, together with density-dependent forage limitation, results in resource competition and a decline in bharal density. Under the present conditions of high livestock density and supplemental feeding, restricting livestock numbers and creating livestock-free areas are necessary measures for conserving Trans-Himalayan wild herbivores. Mediating competitive effects on bharal through supplemental feeding is not a feasible option.
    Plant competition in pest-suppressive intercropping systems complicates evaluation of herbivore responses
    Bukovinszky, T. ; Tréfás, H. ; Lenteren, J.C. van; Vet, L.E.M. ; Fremont, J. - \ 2004
    Agriculture, Ecosystems and Environment 102 (2004). - ISSN 0167-8809 - p. 185 - 196.
    brevicoryne-brassicae l - host-plant - population-dynamics - cruciferous plants - brussels-sprouts - pieris-rapae - oviposition - diversity - insect - performance
    In the light of current theories on the effects of intercropping on pest reduction, population responses of the diamondback moth (Plutella xylostella), the cabbage aphid (Brevicoryne brassicae) and the life history traits of the large white butterfly (Pieris brassicae) were studied in a Brussels sprout (Brassica oleracea gemmifera)/malting barley (Hordeum vulgare) additive row intercrop and a Brussels sprout monoculture. More P. xylostella adults were caught in the monoculture than in the intercrop. Numbers of R xylostella larvae and pupae per sprout plant were lower in intercropped plots than in monocultures. However, more larvae and pupae were found per m(2) leaf area in the inter- than in the monocrop. Both the densities per plant and per m(2) leaf area of B. brassicae populations were lower in the inter- than in the monocrop. After the barley withered and competition with Brussels sprout abated, aphid densities became higher in the inter- than in the monocrop. These findings may be explained by interspecific plant competition resulting in stressed sprout plants with a smaller size and delayed phenology relative to monocropped plants. Effects of differences in plant nutritional quality on herbivore performance were studied by offering leaves of inter- and monocropped sprout plants to larval R brassicae. Performance and food utilisation were significantly better on leaves from the intercrop, (lower dry weight consumption, higher growth rates) than from the monocrop. Defoliation rate was also higher on leaves of intercropped plants than on monocropped ones. The studies indicate that plant stress and consequent changes in developmental rate and nutritional quality of plants are playing a role in herbivore population responses to intercropping. It is argued that such confounding effects of plant competition in intercropping designs can hamper the evaluation of herbivore responses in pest-suppressive agro-ecosystems. (C) 2003 Elsevier B.V. All rights reserved.
    The effect of spatial distribution of mycoparasites on biocontrol efficacy: a modelling approach
    Jeger, M.J. ; Termorshuizen, A.J. ; Nagtzaam, M.P.M. ; Vandenbosch, F. - \ 2004
    Biocontrol Science and Technology 14 (2004)4. - ISSN 0958-3157 - p. 359 - 373.
    sclerotinia lettuce drop - sporidesmium-sclerotivorum - biological-control - rhizoctonia-solani - population-dynamics - soil-moisture - growth - field - host - pathogen
    The spatial distribution of propagules in soil is an important factor in determining the ability of mycoparasites to control soilborne plant pathogens. The assumptions of uniform, random and aggregated propagule distribution were used to evaluate the importance of spatial distribution patterns of propagules of a mycoparasite. For the random and uniform cases explicit expressions were obtained for the average distance between propagules. Average distances among propagules are 40-50% smaller for the random compared to the uniform distribution. For the aggregated case no explicit expression is possible and numerical simulations were used to generate spatial distributions. The consequences for host inactivation by the mycoparasite were evaluated using a simple model of omnidirectional and constant growth of the mycoparasite. A random distribution of propagules gave a considerably slower rate of inactivation than the uniform distribution. Numerical simulations were made to generate comparable patterns of host inactivation for aggregated distributions in which propagule clusters were located at random in three-dimensional space and the distances between propagules with centres followed a normal distribution. The number of propagule centres and propagules/centre varied for a given inoculum density. Parameters were estimated from published data for sclerotia of Sclerotium minor inactivation at different densities of macroconidia of Sporidesmium sclerotivorum. Differences in host inactivation between the uniform and random distributions were small but both gave poor predictions of the field data at low and high densities. The aggregated distribution gave an improved fit for the higher propagule densities but no improvement at the lower. In studying the dynamics of mycoparasites it may be more significant epidemiologically to design treatments based on differences in mean distances between propagules rather than population densities. Density-dependent effects on growth rate need more attention in models and studies on mycoparasite ecology.
    Sediment pollution and predation affect structure and production of benthic macroinvertebrate communities in the Rhine-Meuse delta, The Netherlands
    Lange, H.J. de; Jonge, J. de; Besten, P.J. den; Oosterbaan, J. ; Peeters, E.T.H.M. - \ 2004
    Journal of the North American Benthological Society 23 (2004)3. - ISSN 0887-3593 - p. 557 - 579.
    waterverontreiniging - waterinvertebraten - zware metalen - sediment - besmetters - stroomvlakten - predatie - toxicologie - nederland - ecotoxicologie - rijn - maas - zuid-holland - water pollution - aquatic invertebrates - heavy metals - sediment - contaminants - floodplains - predation - toxicology - netherlands - ecotoxicology - river rhine - river meuse - zuid-holland - saint-francois quebec - acid volatile sulfide - invertebrate community - toxicological factors - population-dynamics - floodplain lakes - fresh-water - availability - bioavailability - extraction
    Most floodplain sediments of the rivers Rhine and Meuse in The Netherlands are moderately polluted with trace metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other chemicals. The effects of these sediment-bound contaminants on the productivity of benthic macroinvertebrates are unclear. Sixteen locations along a pollution gradient were investigated in creeks in the Biesbosch floodplain area. Sediment samples were analyzed for bulk sediment characteristics and contaminants (total and bioavailable concentrations of trace metals, PAHs, and PCBs). Exclosures were used to study the effect of predation by fish and birds on macroinvertebrates. Macroinvertebrates were sampled and identified to species level, and production was estimated from biomass increases inside the exclosures during a 1-mo interval in spring
    Most floodplain sediments of the rivers Rhine and Meuse in The Netherlands are moderately polluted with trace metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other chemicals. The effects of these sediment-bound contaminants on the productivity of benthic macroinvertebrates are unclear. Sixteen locations along a pollution gradient were investigated in creeks in the Biesbosch floodplain area. Sediment samples were analyzed for bulk sediment characteristics and contaminants (total and bioavailable concentrations of trace metals, PAHs, and PCBs). Exclosures were used to study the effect of predation by fish and birds on macroinvertebrates. Macroinvertebrates were sampled and identified to species level, and production was estimated from biomass increases inside the exclosures during a 1-mo interval in spring. Benthic macroinvertebrate species richness was negatively affected by sediment contamination. Production of oligochaetes and chironomids was not correlated with levels of contamination, but production of gastropods was negatively correlated with contamination. Environmental variables that reflected food availability (seston and sediment organic C) were positively correlated with contamination. Predation significantly reduced invertebrate biomass, but the effects of predation and sediment contamination were not correlated with each other. Our study suggested that the moderate levels of contamination affected the structure but not the productivity of the benthic macroinvertebrate community, probably because of the counteracting effects of contamination and associated surplus of food.
    Temporal and spatial distribution of microcrustacean zooplankton in relation to turbidity and other environmental factors in a large tropical lake (L. Tana, Ethiopia)
    Dejen, E. ; Vijverberg, J. ; Nagelkerke, L.A.J. ; Sibbing, F.A. - \ 2004
    Hydrobiologia 513 (2004)1-3. - ISSN 0018-8158 - p. 39 - 49.
    barbs barbus-humilis - aquatic organisms - suspended clay - population-dynamics - community structure - reservoir - reproduction - cladocerans - abundance - dispersal
    The spatial and seasonal distribution of microcrustacean zooplankton of Lake Tana (Ethiopia) was monthly studied for 2 years. Concurrently, various environmental parameters were measured and related to zooplankton distribution. Canonical Correspondence Analysis (CCA) was used to estimate the influence of abiotic factors and chlorophyll a content in structuring the zooplankton assemblage. Among the environmental factors, zooplankton abundance correlated most strongly with turbidity. Turbidity was negatively correlated with species abundance, especially for Daphnia spp. and to the least extent for Diaphanosoma spp. Analysis of variance (ANOVA) was used to determine spatial (littoral, sublittoral and pelagic zone) and temporal (four seasons) variation in zooplankton abundance. We observed significant temporal differences in zooplankton abundance, with highest densities during dry season (November-April). Only cladocerans showed significant differences in habitat use (highest densities in the sublittoral zone).
    Do competition and selective herbivory cause replacement of Phragmites australis by tall forbs?
    Lenssen, J.P.M. ; Menting, F.B.J. ; Putten, W.H. van der - \ 2004
    Aquatic Botany 78 (2004)3. - ISSN 0304-3770 - p. 217 - 232.
    marsh plant zonation - salt-marsh - population-dynamics - community structure - nutrient dynamics - diverse habitats - insect herbivore - field experiment - shoot density - clonal plant
    We investigated the role of biotic factors in determining abundance of the low marsh species Phragmites australis and the high marsh species Epilobium hirsutum. In a 2-year field experiment, at a position where Phragmites and Epilobium co-occurred, responses of both species to each other's removal were measured. In the second year, we also tested if larvae of Archanara geminipuncta, which feed exclusively on Phragmites shoots, affect the competitive ability of Phragmites relative to Epilobium. For both species, removal of aboveground material by clipping did not enhance shoot size or decrease variability in shoot size of the removed species itself. Surprisingly however, shoot numbers of both species increased after removal of the other, which demonstrates that there was a mutual inhibition of each other's abundance. Comparing the responses of Archanara-infested and non-infested Phragmites shoots revealed no increased competitive suppression by Epilobium due to selective herbivory. Instead, we found that herbivore activity was lower in plots with Epilobium, which demonstrates that Archanara population size is reduced by the presence of non-host plant species. These results contradict the common assumption that biotic factors constrain a species upper limit along flooding gradients. Instead, our result suggest that different biotic interactions may counteract each other and thus slow down replacement by successive species. (C) 2003 Elsevier B.V. All rights reserved.
    Climate change meets habitat fragmentation: linking landscape and biogeographical scale levels in research and conservation
    Opdam, P.F.M. ; Wascher, D.M. - \ 2004
    Biological Conservation 117 (2004)3. - ISSN 0006-3207 - p. 285 - 297.
    spatial variation - species richness - agricultural landscapes - population-dynamics - abundance - range - metapopulation - forest - birds - connectivity
    Climate change and habitat fragmentation are considered key pressures on biodiversity. In this paper we explore the potential synergetic effects between these factors. We argue that processes at two levels of spatial scale interact: the metapopulation level and the species range level. Current concepts of spatially dynamic metapopulations and species ranges are consistent, and integration improves our understanding of the interaction of landscape level and geographical range level processes. In landscape zones in which the degree of habitat fragmentation allows persistence, the shifting of ranges is inhibited, but not blocked. In areas where the spatial cohesion of the habitat is below the critical level of metapopulation persistence, the expansion of ranges will be blocked. An increased frequency of large-scale disturbances caused by extreme weather events will cause increasing gaps and an overall contraction of the distribution range, particularly in areas with relatively low levels of spatial cohesion. Taking into account the effects of climate change on metapopulations, habitat distribution and land use changes, future biodiversity research and conservation strategies are facing the challenge to re-orient their focus and scope by integrating spatially and conceptually more dynamic aspects at the landscape level.
    Dynamics of a scrapie outbreak in a flock of Romanov sheep-estimation of transmission parameters
    Hagenaars, T.H.J. ; Donelly, C.A. ; Ferguson, N.M. ; Anderson, R.M. - \ 2003
    Epidemiology and Infection 131 (2003). - ISSN 0950-2688 - p. 1015 - 1022.
    population-dynamics - mathematical-model - great-britain - epidemiology - infection - disease - virus - uk
    Knowledge of epidemiological mechanisms and parameters underlying scrapie transmission in sheep flocks remains very limited at present. Here we introduce a method for fitting stochastic transmission models to outbreak data to estimate bounds on key transmission parameters. We apply this method to data describing an outbreak of scrapie in a closed flock of Romanov sheep. The main findings are that the relative infectiousness of infected animals in this outbreak becomes appreciable early into disease incubation and that the mean incubation period is less than 1·5 years. We also find that the data are consistent with a broad range of values for the basic reproduction number R0 and describe how the boundaries of this range depend on assumptions about the mean incubation period and the contribution to transmission of a long-lived environmental reservoir of infectivity.
    A concept of food-web structure in organic arable farming systems
    Smeding, F.W. ; Snoo, G.R. de - \ 2003
    Landscape and Urban Planning 65 (2003). - ISSN 0169-2046 - p. 219 - 236.
    skylarks alauda arvensis - winter-wheat fields - southern england - population-dynamics - natural enemies - carabid beetles - pest-management - soil - agroecosystems - bioindicators
    A proposal for a descriptive or topological farm food web is derived from field observations and from references in literature. Important themes in the food-web theory are tentatively applied to this preliminary model, explaining differences between local farm food-web structures and how they are related to farm and/or ecological infrastructure (EI) management. Predictions are made for four different farm food-web structures for extremes of farm and environmental gradients corresponding to the length of organic duration and amount/quality of El. The implications with regard to farming practices and nature conservation are that both organic duration and the amount/quality of ecological infrastructure may contribute to ecosystem services and nature conservation. However, an optimisation of the farm food web with regard to ecosystem services, may possibly run counter to nature conservation goals. (C) 2003 Published by Elsevier Science B.V.
    Fo-spectra of chlorophyll fluorescence for the determination of zooplankton grazing
    Lürling, M.F.L.L.W. ; Verschoor, A.M. - \ 2003
    Hydrobiologia 491 (2003). - ISSN 0018-8158 - p. 145 - 157.
    rotifer brachionus-calyciflorus - fresh-water zooplankton - microcystis-aeruginosa - planktonic rotifers - population-dynamics - loosdrecht lakes - clearance rates - feeding rates - growth-rate - food
    In the PHYTO-PAM phytoplankton analyzer the minimal fluorescence of dark-adapted samples (F-0) was assessed, which gives direct information on the chlorophyll-a content. Clearance rates (CR) of Daphnia and Brachionus were calculated from a decrease in chlorophyll-a concentration using the PHYTO-PAM fluorometer for non-sacrificial sampling of chlorophyll-a. Clearance rates of Daphnia were measured and compared with those based on the cell-counts method using an electronic particle counter ( Coulter counter). Chlorophyll fluorescence-based CR for Daphnia magna were very strongly correlated with Coulter-based CR, signifying the potential suitability of the PHYTO-PAM in grazing experiments. A procedure for determination of rotifer clearance rates was developed and the effects of rotifer density, duration of the grazing period, and food concentration on CR were investigated. Between 10 and 30 rotifers in 2.5 ml food suspension (i.e. 4 - 12 rotifers per ml) appeared optimal for calculating CR. The application of the deconvolution of F-0-spectra in food selectivity experiments was evaluated using various mixtures of the green alga Scenedesmus obliquus and the cyanobacterium Microcystis aeruginosa fed to Brachionus. CR for Brachionus on M. aeruginosa were lower than on S. obliquus but this was not caused by toxicity, because no mortality was observed. The higher CR on Scenedesmus than on Microcystis in the mixtures suggested selectivity. The importance of digital suppression of background fluorescence is highlighted in additional experiments with Daphnia feeding on mixtures of Microcystis and Scenedesmus, or on Microcystis alone. Without background correction of filtered samples, negative clearance rates were obtained for the 'blue' Microcystis signal. Soluble fluorescing compounds of cyanobacterial origin, phycocyanin, were released from the Daphnia and contributed 40% to the overall-fluorescence. Deconvolution of F-0-spectra for the determination of chlorophyll-a using the PHYTO-PAM appears to be a suitable tool for determination of rotifer CR even at very low food concentrations. A drawback of the method is that rather high rotifer densities are required. The required grazing period, however, is shorter than for cell-count methods, the method is sensitive, clearance rates can be measured at low food concentrations (
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