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
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