SYMP 4-4: Consequences of adaptive foragers in complex model communities
Nicolas Loeuille, Universite Paris 6, Michel Loreau, McGill University, Ake Brannstrom, University of Umea, and Ulf Dieckmann, International Institute for Applied Systems Analysis.
While models including few interacting species provide useful bases for understanding the effects of adaptive foragers, natural systems always contain many species in interaction. Therefore, it is important to get a grasp on the effects of adaptation when this complexity is accounted for. When the number of interactions is large, the possibilities of indirect evolutionary and demographic effects of the adaptation of a given species on any other species of the community are numerous. It is, for example, possible to focus on changes in a few traits such as diet choice (e.g., optimal foraging) or body size. Both traits have large impacts on competitive and trophic interactions, so that adaptive changes in one of these traits is likely to affect the interaction net of the community. Interestingly, adaptation acting on these traits allows the emergence of large scale patterns in the community. The evolution of body size may yield the emergence of whole food webs whose characteristics (connectance, food chain length, omnivory etc...) are comparable to those observed in empirical datasets. Diet choice also constrains the values that the connectance of the whole system can take. This provides a mechanistic explanation for the low variability of connectance that is observed in nature. These two models provide explicit links between adaptation (evolution in the first case, behavior in the second) acting at individual scale and community scale patterns. Adaptation may also play a role in the diversity-stability debate. Food webs produced by the evolution of body size may be very diverse and are stable. Similarly, when diet choice is considered, it is possible to get positive relationships between the total diversity and the stability of the community. Adaptation, either evolution or behavioral changes, is a dynamical process driving the structures and changes observed in communities.