PARENT SESSION
Contributed Oral Session 14: Evolutionary Ecology: Theory; Modeling
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal
Niche or neutrality: the continuum hypothesis.
Dominique, Gravel*,1, Canham, Charles*,2, Marilou, Beaudet*,1, Christian, Messier*,1, 1 Université du Québec à Montréal, Montréal, Québec, Canada2 Institute of Ecosystem Studies, Millbrook, New York, United States
ABSTRACT- Community ecology is rich in numerous hypotheses explaining species coexistence. Some form of niche differentiation is the basis for a vast majority of coexistence mechanisms and the focus of most empirical studies. Neutral models have challenged community ecologists in recent years because they predict the broad outlines of diversity patterns while they are based on highly simplified assumptions. Instead of pursuing falsification of neutral models, we ask if community dynamics can be described along a continuum between niche and neutrality. Under this perspective, a more general theory of coexistence would provide mechanisms placing a community somewhere along this continuum. Here we show with a spatially explicit community model that such a continuum can occur as a consequence of recruitment limitation. We found that, even in the presence of a strong niche differentiation, a gradient of recruitment limitation increases stochasticity and reduces similarity between replicate runs of the model with identical underlying dynamics. Our results also show that the continuum between niche and neutral is an increasing function of the species richness of the community. However, contrary to many suggestions in the literature, an increase in dispersal distance also leads to an increase in stochasticity. This result is explained by the strong interaction between dispersal and the spatial structure of the environment. Although a short dispersal distance will increase the likelihood of vacant sites at long distance, it tends to help species to guard the most favourable sites against stochastic invasion. In agreement with this result, we also found that any environmental heterogeneity that would increase a spatial storage effect, such as coarse grain spatial structure, will increase the determinism of community dynamics. A major prediction from the hypothesis developed here is that highly diverse ecosystems are more subject to a neutral assemblage than less diverse ones. This could solve the paradox between the observation of species differentiation in highly diverse communities and the correspondence of their structure to any predictions made by neutral models.
Key words: Ecological niche, Neutral theory, Coexistence