SG: Identifying patterns of trait variation that arise from competitive interactions

Yale University, New Haven CT

Investigators

Abstract

Competition for scarce resources is a fundamental aspect of life on earth. Terrestrial plants compete for light, water and soil nutrients. Many birds compete for access to food and nesting sites, and in the intertidal zone, shellfish compete for rocky substrate on which to attach themselves. Classic ecological theory predicts that when competition is important, species can coexist with others by having traits that differentiate their resource needs from those of their competitors. In turn, this prediction has led to the hypothesis that when communities comprise well differentiated species, competition must be a dominant process. Unfortunately, this hypothesis does not support key aspects of modern coexistence theory, which has demonstrated that even very similar competing species can coexist if the competitive advantage is small. This project will address this scientific controversy by developing a general eco-evolutionary mathematical model of intraspecific competition in which competition is explicitly linked to species traits and evolutionarily stable communities are identified. Ultimately, this work will lead to a better understanding of the distribution and abundance of organisms in natural communities and resolve these discrepancies in classic and modern theory. Additionally, this research will provide research training for a postdoctoral researcher and an undergraduate student. A teaching module in theoretical ecology will also be developed for undergraduate and graduate students. Most of the theoretical work on trait distributions arising from competitive interactions has assumed that a single trait (or at most a pair of traits) determines both the niche overlap and any fitness differences among competitors. Under this assumption, trait distributions of climax communities generally demonstrate over-dispersion; however, it has also been shown that clumps of similar species can form at intermediate time-scales when their fitness differences are small (termed "emergent neutrality"). This project will employ mathematical models of competition to compare patterns of trait variation that emerge under modern coexistence theory to data collected from natural communities. This project will incorporate a greater degree of biological realism than previous approaches, by modulating the extent to which niche differences and fitness differences are controlled by the same trait or different traits. Numerical simulations of a Lotka-Volterra competition model within an eco-evolutionary framework will be used to identify evolutionarily stable communities. The patterns of trait dispersion that develop will be summarized using a variety of metrics to demonstrate the patterns and mechanisms that underlie climax communities when traits have varying degrees of control over fitness. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.