Biomedical subjects

Nicolas Loeuille

Publications and source records attributed to Nicolas Loeuille.

5 recordsLinked to original sources

PubMed2006

Evolution of body size in food webs: does the energetic equivalence rule hold?

The energetic equivalence rule (EER), which is derived from empirical observations linking population density and body size and from the allometric law linking metabolism and body size, predicts that the amount of energy used by the various species should be independent of body size. Here, we examine this hypothesis using a model that allows entire food webs to emerge from coevolution of interacting species. Body size influences both individual metabolism and interactions among species in the model. Overall, population density does decrease with body size roughly following a power law whose exponent is variable. We discuss this variability in the light of empirical data sets. The emerging relationship between the flux of resources exploited by the various species and their body size follows a decreasing power law, thus contradicting the EER. Our model emphasizes the importance of considering the influence of body size on species interactions in attempting to explain large-scale patterns related to body size.

Animals↗

PubMed2005

Evolutionary emergence of size-structured food webs.

Explaining the structure of terrestrial and aquatic food webs remains one of the most important challenges of ecological theory. Most existing models use emergent properties of food webs, such as diversity and connectance as parameters, to determine other food-web descriptors. Lower-level processes, in particular adaptation (whether by behavioral, developmental, or evolutionary mechanisms), are usually not considered. Here, we show that complex, realistic food webs may emerge by evolution from a single ancestor based on very simple ecological and evolutionary rules. In our model, adaptation acts on body size, whose impact on the metabolism and interactions of organisms is well established. Based on parameters defined at the organism scale, the model predicts emergent properties at the food-web scale. Variations of two key parameters (width of consumption niche and competition intensity) allow very different food-web structures and functionings to emerge, which are similar to those observed in some of the best-documented food webs.

Adaptation, Biological↗

PubMed2004

Intrinsic and climatic factors in North-American animal population dynamics.

BACKGROUND: Extensive work has been done to identify and explain multi-year cycles in animal populations. Several attempts have been made to relate these to climatic cycles. We use advanced time series analysis methods to attribute cyclicities in several North-American mammal species to abiotic vs. biotic factors. RESULTS: We study eleven century-long time series of fur-counts and three climatic records--the North Atlantic Oscillation (NAO), the El-Niño-Southern Oscillation (ENSO), and Northern Hemisphere (NH) temperatures--that extend over the same time interval. Several complementary methods of spectral analysis are applied to these 14 times series, singly or jointly. These spectral analyses were applied to the leading principal components (PCs) of the data sets. The use of both PC analysis and spectral analysis helps distinguish external from intrinsic factors that influence the dynamics of the mammal populations. CONCLUSIONS: Our results show that all three climatic indices influence the animal-population dynamics: they explain a substantial part of the variance in the fur-counts and share characteristic periods with the fur-count data set. In addition to the climate-related periods, the fur-count time series also contain a significant 3-year period that is, in all likelihood, caused by biological interactions.

Animals↗

PubMed2004

Nutrient enrichment and food chains: can evolution buffer top-down control?

We show how evolutionary dynamics can alter the predictions of classical models of the effects of nutrient enrichment on food webs. We compare an ecological nutrient-plant-herbivore food-chain model without evolution with the same model, including herbivore evolution, plant evolution, or both. When only herbivores are allowed to evolve, the predictions are similar to those of the ecological model without evolution, i.e., plant biomass does not change with nutrient addition. When only plants evolve, nutrient enrichment leads to an increase in the biomass of all compartments. In contrast, when plants and herbivores are allowed to coevolve, although these two classical patterns are common, a wide variety of other responses is possible. The form of the trade-offs that constrain evolution of the two protagonists is then critical. This stresses the need for experimental data on phenotypic traits, their costs and their influence on the interactions between organisms and the rest of the community.

Adaptation, Biological↗

PubMed2002

Consequences of plant-herbivore coevolution on the dynamics and functioning of ecosystems.

The potential consequences of plant-herbivore coevolution for ecosystem functioning are investigated using a simple nutrient-limited ecosystem model in which plant and herbivore traits are subject to adaptive dynamics. Although the ecological model is very simple and always reaches a stable equilibrium in the absence of evolution, coevolution can generate a great diversity of dynamical behaviors. The evolutionary dynamics can lead to a stable equilibrium. If the evolution of plants is fast enough, certain values of the trade-off parameters lead to complex evolutionary cycles bounded by physiological constraints. The dynamical behavior of the model is very different when the dynamics of inorganic nutrient is ignored and plant competition is modeled by a logistic growth function. This emphasizes the importance of including explicit nutrient dynamics in studies of plant-herbivore coevolution.

Adaptation, Biological↗