The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Jouni K. Nieminen - One of the best experts on this subject based on the ideXlab platform.
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no evidence of sensitivity to Initial Population Size in a fungus nematode soil food chain
Soil Biology & Biochemistry, 2002Co-Authors: Jouni K. NieminenAbstract:Abstract Population dynamics are modeled by nonlinear differential equations. However, sensitive dependence on Initial Population Size, which is typical of such models, is rarely taken into account by experimentalists. Three microcosm experiments are reported showing that the final Population density of a common fungal-feeding nematode is not sensitive to the Initial Population Size. One experiment was conducted in sterilized humus soil in which the fungus–nematode food chain became limited by carbon. Two parallel experiments were conducted in fertilized mineral soil kept nutrient-limited by adding glucose. An Initially even distribution of Population Sizes was converted into a normal or normalizable unimodal distribution in all three experiments. The results support a view that the variation in final Population Size was due to stochasticity and measurement error rather than dynamic instability.
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No evidence of sensitivity to Initial Population Size in a fungus–nematode soil food chain
Soil Biology and Biochemistry, 2002Co-Authors: Jouni K. NieminenAbstract:Abstract Population dynamics are modeled by nonlinear differential equations. However, sensitive dependence on Initial Population Size, which is typical of such models, is rarely taken into account by experimentalists. Three microcosm experiments are reported showing that the final Population density of a common fungal-feeding nematode is not sensitive to the Initial Population Size. One experiment was conducted in sterilized humus soil in which the fungus–nematode food chain became limited by carbon. Two parallel experiments were conducted in fertilized mineral soil kept nutrient-limited by adding glucose. An Initially even distribution of Population Sizes was converted into a normal or normalizable unimodal distribution in all three experiments. The results support a view that the variation in final Population Size was due to stochasticity and measurement error rather than dynamic instability.
Vincent Bretagnolle - One of the best experts on this subject based on the ideXlab platform.
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viability of the endangered little bustard tetrax tetrax Population of western france
Biodiversity and Conservation, 2005Co-Authors: Manuel B Morales, Vincent Bretagnolle, Beatriz ArroyoAbstract:Stochastic computer simulations are used to evaluate the sensitivity of Little bustard Population parameters, estimating the survival probabilities of the seven endangered Little bustard Populations of central-western France for which conservation actions are currentlybeing or have been implemented. Different scenarios of parameter compensation for those nuclei to establish parameter levels assuring Population viability are discussed. Adult survival, productivity per female, Initial Population Size and carrying capacity were the most sensitive parameters in a hypothetical, isolated Population. Juvenile survival also affected Population survival, although its sensitivity was lower. Sex ratio did not have a linear effect on Population survival, but probability of extinction increased for extreme values. Productivity per female and Initial Population Size, varied strongly among the Populations studied, determining their average time of extinction and growth rate. When a metaPopulation scenario was simulated, the survival probabilities of each Population and the metaPopulations stayed close to 1.0 if no mortality was associated to migration. When mortality during migration was included in the simulations, the metaPopulation's probability of survival significantly decreased under 90%. This approach may help managers to correctly address conservation measures and design effective strategies, which should be directed mainly to improve productivity, enhance female survival, and minimise mortality during migration (e.g. promoting insect-rich nesting substrates, avoiding female killing and nest destruction at harvesting, reducing the risk of collision with powerlines, or controlling poaching).
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Predicting short-term extinction risk for the declining Little Bustard (Tetrax tetrax) in intensive agricultural habitats
Biological Conservation, 2005Co-Authors: Pablo Inchausti, Vincent BretagnolleAbstract:Populations of Little Bustard (Tetrax tetrax) have shown pronounced declines in European farmland landscapes over the last 25 years due to the intensification of agricultural practices. In France, the number of breeding males in agricultural habitats has declined by 92% since 1980 as a result of decreases in insect abundance and nest destruction during harvesting. We formulate an age- and sex-structured stochastic model for the remaining Little Bustard Population in SW France that has been studied since 1997 and, using actual values of demographic rates, we estimate its extinction risk over a time period of 30 years to be of 0.45. At the level of local Populations, the extinction risk ranged between 0.66 and 0.90, largely depending on the Initial Population Size and local fecundity of each Population. A comprehensive sensitivity analysis evaluated the influence of uncertain demographic rates and of aspects of the spatial dynamics (sex and age dispersing individuals, sex-biased dispersal and different dispersal rates) on the predicted extinction risks and showed that our model was robust to changes of a wide range of combinations assessed. Given the severity of the current decline, and the spatial issues raised by our analysis, implications of our findings for the conservation of this endangered species are suggested.
Elodie Vercken - One of the best experts on this subject based on the ideXlab platform.
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The highs and lows of dispersal: how connectivity and Initial Population Size jointly shape establishment dynamics in discrete landscapes
Oikos, 2015Co-Authors: Thibaut Morel-journel, Pierre Girod, Ludovic Mailleret, Alexandra Auguste, Aurélie Blin, Elodie VerckenAbstract:Identifying the main factors driving introduced Populations to establishment is a major challenge of invasion biology. Due to their small Initial Size, introduced Populations are most vulnerable to extinction because of demographic stochasticity or Allee effects. While an increase in Initial Population Size is known to increase establishment success, much remains to be understood regarding its interplay with connectivity in spatially structured environments. In order to better understand how demographic mechanisms interact at such spatial scale, we developed a stochastic model of Population dynamics in discrete space to investigate the effect of connectivity and Initial Population Size on establishment. The predictions derived from the model were then tested using experimental introductions of an insect parasitoid (Trichogramma chilonis) in spatially structured laboratory microcosms. Both theoretical and experimental results demonstrated that the connectivity of the introduction site had 1) a deleterious effect in the first generation when the introduced Population was small and 2) a beneficial impact brought about by metaPopulation effects in the subsequent generations. Interestingly, Populations displayed a weakly pushed invasion pattern promoting early establishment, which was mainly underpinned by dispersal stochasticity and the discrete nature of the landscape. These results shed light on the critical influence of landscape connectivity on establishment dynamics.
Thibaut Morel-journel - One of the best experts on this subject based on the ideXlab platform.
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The highs and lows of dispersal: how connectivity and Initial Population Size jointly shape establishment dynamics in discrete landscapes
Oikos, 2015Co-Authors: Thibaut Morel-journel, Pierre Girod, Ludovic Mailleret, Alexandra Auguste, Aurélie Blin, Elodie VerckenAbstract:Identifying the main factors driving introduced Populations to establishment is a major challenge of invasion biology. Due to their small Initial Size, introduced Populations are most vulnerable to extinction because of demographic stochasticity or Allee effects. While an increase in Initial Population Size is known to increase establishment success, much remains to be understood regarding its interplay with connectivity in spatially structured environments. In order to better understand how demographic mechanisms interact at such spatial scale, we developed a stochastic model of Population dynamics in discrete space to investigate the effect of connectivity and Initial Population Size on establishment. The predictions derived from the model were then tested using experimental introductions of an insect parasitoid (Trichogramma chilonis) in spatially structured laboratory microcosms. Both theoretical and experimental results demonstrated that the connectivity of the introduction site had 1) a deleterious effect in the first generation when the introduced Population was small and 2) a beneficial impact brought about by metaPopulation effects in the subsequent generations. Interestingly, Populations displayed a weakly pushed invasion pattern promoting early establishment, which was mainly underpinned by dispersal stochasticity and the discrete nature of the landscape. These results shed light on the critical influence of landscape connectivity on establishment dynamics.
Beatriz Arroyo - One of the best experts on this subject based on the ideXlab platform.
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viability of the endangered little bustard tetrax tetrax Population of western france
Biodiversity and Conservation, 2005Co-Authors: Manuel B Morales, Vincent Bretagnolle, Beatriz ArroyoAbstract:Stochastic computer simulations are used to evaluate the sensitivity of Little bustard Population parameters, estimating the survival probabilities of the seven endangered Little bustard Populations of central-western France for which conservation actions are currentlybeing or have been implemented. Different scenarios of parameter compensation for those nuclei to establish parameter levels assuring Population viability are discussed. Adult survival, productivity per female, Initial Population Size and carrying capacity were the most sensitive parameters in a hypothetical, isolated Population. Juvenile survival also affected Population survival, although its sensitivity was lower. Sex ratio did not have a linear effect on Population survival, but probability of extinction increased for extreme values. Productivity per female and Initial Population Size, varied strongly among the Populations studied, determining their average time of extinction and growth rate. When a metaPopulation scenario was simulated, the survival probabilities of each Population and the metaPopulations stayed close to 1.0 if no mortality was associated to migration. When mortality during migration was included in the simulations, the metaPopulation's probability of survival significantly decreased under 90%. This approach may help managers to correctly address conservation measures and design effective strategies, which should be directed mainly to improve productivity, enhance female survival, and minimise mortality during migration (e.g. promoting insect-rich nesting substrates, avoiding female killing and nest destruction at harvesting, reducing the risk of collision with powerlines, or controlling poaching).