Funded Grants

Uncovering mechanisms of diversity maintenance: the interplay between abiotic environmental variation and non-linear biotic interactions

Homage to Santa Rosalia, or why are there so many kinds of animals?"

In 1959, Evelyn Hutchinson posed the question that remains a central puzzle in ecology and evolutionary biology: how could a large number of species be supported by a seemingly small number of limiting resources? There are many answers to this question, some more satisfying than others, but none that fully addresses the many complexities and contradictions that this problem poses. I pursue this question because of my fascination with the fundamental issue that underlies it: how do non-linear feedback processes operating at multiple levels of a dynamical system interact with sources of variation that are outside the system's feedback structure to determine overall system properties?

Diversity results from the interplay between abiotic environmental variation (e.g., temperature, humidity, nutrient availability) and the non-linear feedback processes (e.g., density- or frequency-dependence) that underlie biotic interactions (e.g., competition, predation, mutualisms). Elucidating the mechanisms that drive this interplay involves a three-step process. First, one needs to understand how abiotic environmental variation affects the key life history (e.g., fecundity, development, survivorship) and interaction (e.g., attack rates, competition coefficients) traits of organisms. Second, one needs to determine how trait responses to environmental variation translate into population-level responses (e.g., per capita growth rates) via the positive and negative feedback processes that underlie interactions within and between species. Third, one needs to elucidate how the population-level responses feed back to the trait response, causing the latter to evolve both in response to abiotic environmental variation and the biotic selective environment provided by resources, mutualists and natural enemies. These are the core issues that drive my research program. I pursue them because they are essential to obtaining a comprehensive understanding of the mechanisms that maintain diversity.

The interplay between abiotic environmental variation and non-linear biotic interactions involves multiple levels of organization (traits, individuals, populations and communities) with feedback processes operating at each level. For instance, different trait types (e.g., life history vs. interaction traits) exhibit different types of non-linear responses to environmental variation. The net effect of such multiple non-linear responses, which manifests as a demographic response at the organismal level, are highly non-additive. These demographic responses (e.g., per capita birth and death rates) in turn drive the non-linear feedbacks arising from interactions within species (e.g., competition) that lead to population regulation (via negative feedback processes) and interactions between species (e.g., competition, predation, mutualisms) that lead to species coexistence (via negative feedback overriding positive feedback). To complete the picture, we need to add one more level of complexity: the feedback between ecological dynamics (population regulation and species interactions) and selection on trait responses driven by both abiotic variation and biotic interactions. Thus we have a complex system (community) whose properties are driven by the interplay between environmental variability and non-linear feedbacks at multiple levels (traits, individuals, populations) and dynamics at multiple scales (ecological and evolutionary). My research therefore falls easily within the purview of the complex systems science that the Foundation envisions.