The Experts below are selected from a list of 214632 Experts worldwide ranked by ideXlab platform
David Choquenot - One of the best experts on this subject based on the ideXlab platform.
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Landscape complementation and food limitation of large herbivores: habitat-related constraints on the foraging efficiency of wild pigs
Journal of Animal Ecology, 2003Co-Authors: David Choquenot, Wendy A. RuscoeAbstract:Summary 1 The effect that the proximity of habitats containing essential resources has on animal abundance at large spatial scales is called landscape complementation. Landscape complementation can influence interaction between large herbivores and their food resources where the proximity of habitats containing essential resources constrains their foraging or demographic efficiency. 2 We tested the effect that the proximity of a thermal refuge (riverine woodlands) had on interaction between wild pigs and their food resources (pasture). The Numerical Response of pigs (Sus scrofa L.) (estimated as r quarter−1) to pasture biomass was contrasted between four sites that were progressively more isolated from a major floodplain containing extensive areas of riverine woodland. To test whether proximity to riverine woodlands affected the Numerical Response of pigs through a constraint on foraging efficiency, we contrasted the Numerical Response of pigs between the four areas as pasture biomass declined. To test whether pigs exploited riverine woodlands primarily as a thermal refuge, we contrasted the Numerical Response of pigs between the four areas in different seasons. 3 We found that although pasture biomass was similar in the four areas, r was lower than expected for given pasture biomass on the two areas further away from riverine woodlands. We also found that while the effect that proximity to riverine woodlands had on the Numerical Response of pigs became more pronounced when pasture biomass was low, it was not significantly affected by season. 4 These results suggest that the need to access riverine woodlands compromises the foraging efficiency of wild pigs when the distance to this habitat is relatively high, but that the need to access this habitat may not be purely related to thermoregulation. 5 We developed a simple mechanistic model that allows the effects of landscape complementation on herbivore foraging and demographic efficiency to be estimated, and used the model to predict the effect that proximity to riverine woodlands would have on variation in pig density. The model suggests that wild pigs cannot persist in areas more then 10 km from extensive riverine woodlands, unless those areas are periodically re-colonized. This suggests that at the margin of their range around inland river systems, given locations that can be occupied by wild pigs will vary temporally between being sources, pseudosinks and sinks.
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The Numerical Response: rate of increase and food limitation in herbivores and predators
Philosophical Transactions of the Royal Society B, 2002Co-Authors: Peter Bayliss, David ChoquenotAbstract:Two types of Numerical Response function have evolved since Solomon first introduced the term to generalize features of Lotka-Volterra predator-prey models: (i) the demographic Numerical Response, which links change in consumer demographic rates to food availability; and (ii) the isocline Numerical Response, which links consumer abundance per se to food availability. These Numerical Responses are interchangeable because both recognize negative feedback loops between consumer and food abundance resulting in population regulation. We review how demographic and isocline Numerical Responses have been used to enhance our understanding of population regulation of kangaroos and possums, and argue that their utility may be increased by explicitly accounting for non-equilibrium dynamics (due to environmental variability and/or biological interactions) and the existence of multiple limiting factors. Interferential Numerical Response functions may help bridge three major historical dichotomies in population ecology (equilibrium versus non-equilibrium dynamics, extrinsic versus intrinsic regulation and demographic versus isocline Numerical Responses).
Michael Begon - One of the best experts on this subject based on the ideXlab platform.
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disease dynamics in cyclic populations of field voles microtus agrestis cowpox virus and vole tuberculosis mycobacterium microti
Proceedings of The Royal Society B: Biological Sciences, 2004Co-Authors: Rachel Cavanagh, Isla M. Graham, Dick Van Soolingen, Malcolm J Bennett, Torbjorn Ergon, Michael BegonAbstract:The possible role of pathogens in rodent population cycles has been largely neglected since Elton's 'epidemic hypothesis' of 1931. To revisit this question, 12 adjacent, cyclic but out-of-phase populations of field voles (Microtus agrestis) in North East England were studied and the initial results are presented here. The prevalences of antibodies to cowpox virus and of clinical signs of Mycobacterium microti infection (vole tuberculosis) showed delayed (not direct) density dependence (with a lag of three to six months). This did not result from changes in population structure, even though there were such changes associated with the different phases of the cycle. The prevalences rose as vole numbers rose, and peaked as numbers declined. The apparent lag in the Numerical Response of infection prevalence to changes in host abundance is consistent with the hypothesis that diseases, singly or in combination, play a hitherto underestimated role in the dynamics of cyclic populations.
Torbjorn Ergon - One of the best experts on this subject based on the ideXlab platform.
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disease dynamics in cyclic populations of field voles microtus agrestis cowpox virus and vole tuberculosis mycobacterium microti
Proceedings of The Royal Society B: Biological Sciences, 2004Co-Authors: Rachel Cavanagh, Isla M. Graham, Dick Van Soolingen, Malcolm J Bennett, Torbjorn Ergon, Michael BegonAbstract:The possible role of pathogens in rodent population cycles has been largely neglected since Elton's 'epidemic hypothesis' of 1931. To revisit this question, 12 adjacent, cyclic but out-of-phase populations of field voles (Microtus agrestis) in North East England were studied and the initial results are presented here. The prevalences of antibodies to cowpox virus and of clinical signs of Mycobacterium microti infection (vole tuberculosis) showed delayed (not direct) density dependence (with a lag of three to six months). This did not result from changes in population structure, even though there were such changes associated with the different phases of the cycle. The prevalences rose as vole numbers rose, and peaked as numbers declined. The apparent lag in the Numerical Response of infection prevalence to changes in host abundance is consistent with the hypothesis that diseases, singly or in combination, play a hitherto underestimated role in the dynamics of cyclic populations.
Jim Hone - One of the best experts on this subject based on the ideXlab platform.
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climate food density and wildlife population growth rate
Journal of Animal Ecology, 2007Co-Authors: Jim Hone, T H CluttonbrockAbstract:1. The aim of this study was to derive and evaluate a priori models of the relationship between annual instantaneous population growth rate (r) and climate. These were derived from the Numerical Response of annual r and food, and the effect of climate on a parameter in the Numerical Response. The goodness of fit of a range of such deductive models to data on annual r of Soay sheep and red deer were evaluated using information-theoretic (AICc-based) analyses. 2. The analysis for sheep annual r showed negative effects of abundance and negative effects of the interaction of abundance and climate, measured as March rainfall (and winter NAO) in the best fitting models. The analysis for deer annual r showed a negative effect of deer abundance and a positive effect of climate measured as March rainfall (but a negative effect of winter NAO), but no interaction of abundance and climate in the best fitting models. 3. There was most support in the analysis of sheep dynamics for the ratio Numerical Response and the assumption that parameter J (equilibrium food per animal) was influenced by climate. In the analysis of deer dynamics there was most support for the Numerical Responses assuming effects of food and density (Ivlev and density, food and density, and additive Responses) and slightly less support for the ratio Numerical Response. The evaluation of such models would be aided by the collection of and incorporation of food data into the analyses.
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demographic mechanistic and density dependent determinants of population growth rate a case study in an avian predator
Philosophical Transactions of the Royal Society B, 2002Co-Authors: Jim Hone, Richard M SiblyAbstract:Identifying the determinants of population growth rate is a central topic in population ecology. Three approaches (demographic, mechanistic and density-dependent) used historically to describe the determinants of population growth rate are here compared and combined for an avian predator, the barn owl (Tyto alba). The owl population remained approximately stable (r approximately 0) throughout the period from 1979 to 1991. There was no evidence of density dependence as assessed by goodness of fit to logistic population growth. The finite (lambda) and instantaneous (r) population growth rates were significantly positively related to food (field vole) availability. The demographic rates, annual adult mortality, juvenile mortality and annual fecundity were reported to be correlated with vole abundance. The best fit (R(2) = 0.82) Numerical Response of the owl population described a positive effect of food (field voles) and a negative additive effect of owl abundance on r. The Numerical Response of the barn owl population to food availability was estimated from both census and demographic data, with very similar results. Our analysis shows how the demographic and mechanistic determinants of population growth rate are linked; food availability determines demographic rates, and demographic rates determine population growth rate. The effects of food availability on population growth rate are modified by predator abundance.
Rachel Cavanagh - One of the best experts on this subject based on the ideXlab platform.
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disease dynamics in cyclic populations of field voles microtus agrestis cowpox virus and vole tuberculosis mycobacterium microti
Proceedings of The Royal Society B: Biological Sciences, 2004Co-Authors: Rachel Cavanagh, Isla M. Graham, Dick Van Soolingen, Malcolm J Bennett, Torbjorn Ergon, Michael BegonAbstract:The possible role of pathogens in rodent population cycles has been largely neglected since Elton's 'epidemic hypothesis' of 1931. To revisit this question, 12 adjacent, cyclic but out-of-phase populations of field voles (Microtus agrestis) in North East England were studied and the initial results are presented here. The prevalences of antibodies to cowpox virus and of clinical signs of Mycobacterium microti infection (vole tuberculosis) showed delayed (not direct) density dependence (with a lag of three to six months). This did not result from changes in population structure, even though there were such changes associated with the different phases of the cycle. The prevalences rose as vole numbers rose, and peaked as numbers declined. The apparent lag in the Numerical Response of infection prevalence to changes in host abundance is consistent with the hypothesis that diseases, singly or in combination, play a hitherto underestimated role in the dynamics of cyclic populations.
