Center for Biodiversity Theory and Modelling

Moulis-en-Médoc, France

Center for Biodiversity Theory and Modelling

Moulis-en-Médoc, France

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Isbell F.,University of Minnesota | Loreau M.,Center for Biodiversity Theory and Modelling
Ecology and Society | Year: 2014

Humans influence and depend on natural systems worldwide, creating complex societal-ecological feedbacks that make it difficult to assess the long-term sustainability of contemporary human activities. We use ecological niche theory to consider the shortterm (transient) and long-term (equilibrium) effects of improvements in health, agriculture, or efficiency on the abundances of humans, our plant and animal resources, and our natural enemies. We also consider special cases of our model where humans shift to a completely vegetarian diet, or completely eradicate natural enemies. We find that although combinations of health, agriculture, and efficiency improvements tend to support more people and plant resources, they also result in more natural enemies and fewer animal resources. Considering each of these improvements separately reveals that they lead to different, and sometimes opposing, long-term effects. For example, health improvements can reduce pathogen abundances and make it difficult to sustain livestock production, whereas agricultural improvements tend to counterbalance these effects. Our exploratory analysis of a deliberately simple model elucidates trade-offs and feedbacks that could arise from the cascading effects of human activities. © 2014 by the author(s).


Leroux S.J.,McGill University | Leroux S.J.,University of Ottawa | Loreau M.,McGill University | Loreau M.,Center for Biodiversity Theory and Modelling
Ecosystems | Year: 2012

Temporally variable and reciprocal subsidies between ecosystems are ubiquitous. These spatial flows can generate a suite of direct and indirect effects in local and meta-ecosystems. The focus of most subsidy research, however, has been on the response of consumers in recipient ecosystems to constant subsidies over very short or very long time scales. We derive a meta-ecosystem model to explicitly consider the dynamic feedbacks between local ecosystems coupled through reciprocal pulsed subsidies. We predict oscillating reinforcing and dampening effects of reciprocal pulsed herbivore flows. Maximum reinforcing effects between reciprocal pulsed herbivore flows occur when these flows are in phase with the dynamics of neighboring predators. This prediction is robust to a range of pulse quantities and frequencies. Reciprocal pulsed herbivore subsidies lead to spatial and temporal variability in the strength of trophic cascades in local and meta-ecosystems but these cascading effects are the strongest when reciprocal pulsed subsidies are temporally concentrated. When predators demonstrate a behavioral response to prey abundance, reciprocal pulsed subsidies dampen the strength of local trophic cascades but lead to strong trophic cascades across local ecosystems. The timing of reciprocal pulsed subsidies is a critical component that determines the cascading effects of spatial flows. We show that spatial and temporal variabilities in resources and consumers can have a significant influence on the strength of cascading trophic interactions; therefore, our ability to detect and understand trophic cascades may depend on the scale of inquiry of ecological studies. © 2011 Springer Science+Business Media, LLC.


Pillai P.,McGill University | Gonzalez A.,McGill University | Loreau M.,McGill University | Loreau M.,Center for Biodiversity Theory and Modelling
American Naturalist | Year: 2012

Dispersal is crucial to allowing species inhabiting patchy or spatially subdivided habitats to persist globally despite the possibility of frequent local extinctions. Theoretical studies have repeatedly demonstrated that species that exhibit a regional metapopulation structure and are subject to increasing rates of local patch extinctions should experience strong selective pressures to disperse more rapidly despite the costs such increased dispersal would entail in terms of decreased local fitness.We extend these studies to consider how extinctions arising from predator-prey interactions affect the evolution of dispersal for species inhabiting a metacommunity. Specifically, we investigate how increasing a strong extinction-prone interaction between a predator and prey within local patches affects the evolution of each species' dispersal. We found that for the predator, as expected, evolutionarily stable strategy (ESS) dispersal rates increased monotonically in response to increasing local extinctions induced by strong predator top-down effects. Unexpectedly for the prey, however, ESS dispersal rates displayed a nonmonotonic response to increasing predator-induced extinction rates-actually decreasing for a significant range of values. These counterintuitive results arise from how extinctions resulting from trophic interactions play out at different spatial scales: interactions that increase extinction rates of both species locally can, at the same time, decrease the frequency of interaction between the prey and predator at the metacommunity scale. © 2011 by The University of Chicago.


Marleau J.N.,McGill University | Marleau J.N.,Center for Biodiversity Theory and Modelling
Proceedings. Biological sciences / The Royal Society | Year: 2014

The addition of spatial structure to ecological concepts and theories has spurred integration between sub-disciplines within ecology, including community and ecosystem ecology. However, the complexity of spatial models limits their implementation to idealized, regular landscapes. We present a model meta-ecosystem with finite and irregular spatial structure consisting of local nutrient-autotrophs-herbivores ecosystems connected through spatial flows of materials and organisms. We study the effect of spatial flows on stability and ecosystem functions, and provide simple metrics of connectivity that can predict these effects. Our results show that high rates of nutrient and herbivore movement can destabilize local ecosystem dynamics, leading to spatially heterogeneous equilibria or oscillations across the meta-ecosystem, with generally increased meta-ecosystem primary and secondary production. However, the onset and the spatial scale of these emergent dynamics depend heavily on the spatial structure of the meta-ecosystem and on the relative movement rate of the autotrophs. We show how this strong dependence on finite spatial structure eludes commonly used metrics of connectivity, but can be predicted by the eigenvalues and eigenvectors of the connectivity matrix that describe the spatial structure and scale. Our study indicates the need to consider finite-size ecosystems in meta-ecosystem theory.


Marleau J.N.,McGill University | Guichard F.,McGill University | Loreau M.,Center for Biodiversity Theory and Modelling
Proceedings of the Royal Society B: Biological Sciences | Year: 2014

The addition of spatial structure to ecological concepts and theories has spurred integration between sub-disciplines within ecology, including community and ecosystem ecology. However, the complexity of spatial models limits their implementation to idealized, regular landscapes. We present a model meta-ecosystem with finite and irregular spatial structure consisting of local nutrient-autotrophs-herbivores ecosystems connected through spatial flows of materials and organisms. We study the effect of spatial flows on stability and ecosystem functions, and provide simple metrics of connectivity that can predict these effects. Our results show that high rates of nutrient and herbivore movement can destabilize local ecosystem dynamics, leading to spatially heterogeneous equilibria or oscillations across the meta-ecosystem, with generally increased meta-ecosystem primary and secondary production. However, the onset and the spatial scale of these emergent dynamics depend heavily on the spatial structure of the meta-ecosystem and on the relative movement rate of the autotrophs. We show how this strong dependence on finite spatial structure eludes commonly used metrics of connectivity, but can be predicted by the eigenvalues and eigenvectors of the connectivity matrix that describe the spatial structure and scale. Our study indicates the need to consider finite-size ecosystems in meta-ecosystem theory. © 2014 The Author(s) Published by the Royal Society. All rights reserved.


Marleau J.N.,McGill University | Guichard F.,McGill University | Loreau M.,Center for Biodiversity Theory and Modelling
Ecology Letters | Year: 2015

Evidence that ecosystems and primary producers are limited in their productivity by multiple nutrients has caused the traditional nutrient limitation framework to include multiple limiting nutrients. The models built to mimic these responses have invoked local mechanisms at the level of the primary producers. In this paper, we explore an alternative explanation for the emergence of co-limitation by developing a simple, stoichiometrically explicit meta-ecosystem model with two limiting nutrients, autotrophs and herbivores. Our results show that differences in movement rates for the nutrients, autotrophs and herbivores can allow for nutrient co-limitation in biomass response to emerge despite no local mechanisms of nutrient co-limitation. Furthermore, our results provide an explanation to why autotrophs show positive growth responses to nutrients despite 'nominal' top-down control by herbivores. These results suggest that spatial processes can be mechanisms for nutrient co-limitation at local and regional scales, and can help explain anomalous results in the co-limitation literature. © 2015 John Wiley & Sons Ltd/CNRS.


Cherif M.,Umeå University | Loreau M.,Center for Biodiversity Theory and Modelling
Proceedings of the Royal Society B: Biological Sciences | Year: 2013

Plant stoichiometry is thought to have a major influence on how herbivores affect nutrient availability in ecosystems. Most conceptual models predict that plants with high nutrient contents increase nutrient excretion by herbivores, in turn raising nutrient availability. To test this hypothesis, we built a stoichiometrically explicit model that includes a simple but thorough description of the processes of herbivory and decomposition. Our results challenge traditional views of herbivore impacts on nutrient availability in many ways. They show that the relationship between plant nutrient content and the impact of herbivores predicted by conceptualmodels holds only at high plant nutrient contents.At lowplant nutrient contents, the impact of herbivores ismediated by the mineralization/immobilization of nutrients by decomposers and by the type of resource limiting the growth of decomposers. Both parameters are functions of the mismatch between plant and decomposer stoichiometries. Our work provides new predictions about the impacts of herbivores on ecosystemfertility that depend on critical interactions between plant, herbivore and decomposer stoichiometries in ecosystems. © 2013 The Author(s) Published by the Royal Society.


Revilla T.A.,Center for Biodiversity Theory and Modelling | Encinas-Viso F.,CSIRO | Loreau M.,Center for Biodiversity Theory and Modelling
Oikos | Year: 2015

Climate change can alter species phenologies and therefore disrupt species interactions. Habitat destruction can damage biodiversity and population viability. However, we still know very little about the potential effects of these two factors on the diversity and structure of interaction networks when both act simultaneously. Here we developed a mutualistic metacommunity model to explore the effects of habitat destruction and phenological changes on the diversity and structure of plant-pollinator networks. Using an empirical data set of plant and pollinator interactions and their duration in days, we simulated increasing levels of habitat destruction, under projected scenarios of phenological shifts as well for historically recorded changes in phenologies. On one hand, we found that habitat destruction causes catastrophic collapse in global diversity, as well as inducing alternative states. On the other hand, phenological shifts tend to make interactions weaker, increasing local extinction rates. Together, habitat destruction and phenological changes act synergistically, making metacommunities even more vulnerable to global collapse. Metacommunities are also more vulnerable to collapses under scenarios of historical change, in which phenologies are shortened, not just shifted. Furthermore, connectance and nestedness tends to decrease gradually with habitat destruction before the global collapse. Small phenological shifts can raise connectance slightly, due novel interactions appearing in a few generalist species, but larger shifts always reduce connectance. We conclude that the robustness of mutualistic metacommunities against habitat destruction can be greatly impaired by the weakening of positive interactions that results from the loss of phenological overlap. © 2014 The Authors.


Haegeman B.,Center for Biodiversity Theory and Modelling | Loreau M.,Center for Biodiversity Theory and Modelling
Ecology Letters | Year: 2014

One of the central questions of metacommunity theory is how dispersal of organisms affects species diversity. Here, we show that the diversity-dispersal relationship should not be studied in isolation of other abiotic and biotic flows in the metacommunity. We study a mechanistic metacommunity model in which consumer species compete for an abiotic or biotic resource. We consider both consumer species specialised to a habitat patch, and generalist species capable of using the resource throughout the metacommunity. We present analytical results for different limiting values of consumer dispersal and resource dispersal, and complement these results with simulations for intermediate dispersal values. Our analysis reveals generic patterns for the combined effects of consumer and resource dispersal on the metacommunity diversity of consumer species, and shows that hump-shaped relationships between local diversity and dispersal are not universal. Diversity-dispersal relationships can also be monotonically increasing or multimodal. Our work is a new step towards a general theory of metacommunity diversity integrating dispersal at multiple trophic levels. © 2013 John Wiley & Sons Ltd/CNRS.


Loreau M.,Center for Biodiversity Theory and Modelling | de Mazancourt C.,Center for Biodiversity Theory and Modelling
Ecology Letters | Year: 2013

There is mounting evidence that biodiversity increases the stability of ecosystem processes in changing environments, but the mechanisms that underlie this effect are still controversial and poorly understood. Here, we extend mechanistic theory of ecosystem stability in competitive communities to clarify the mechanisms underlying diversity-stability relationships. We first explain why, contrary to a widely held belief, interspecific competition should generally play a destabilising role. We then explore the stabilising effect of differences in species' intrinsic rates of natural increase and provide a synthesis of various potentially stabilising mechanisms. Three main mechanisms are likely to operate in the stabilising effects of biodiversity on ecosystem properties: (1) asynchrony of species' intrinsic responses to environmental fluctuations, (2) differences in the speed at which species respond to perturbations, (3) reduction in the strength of competition. The first two mechanisms involve temporal complementarity between species, while the third results from functional complementarity. Additional potential mechanisms include selection effects, behavioural changes resulting from species interactions and mechanisms arising from trophic or non-trophic interactions and spatial heterogeneity. We conclude that mechanistic trait-based approaches are key to predicting the effects of diversity on ecosystem stability and to bringing the old diversity-stability debate to a final resolution. © 2013 John Wiley & Sons Ltd/CNRS.

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