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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    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.
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