How do interactions among species within an ecological community influence the response of the community to environmental perturbations? This is a central question in understanding how community structure affects the resistance and resilience of ecosystems. I am particularly interested in the application of stochastic models to multispecies data sets, using patterns of population fluctuations to explore the consequences of species interactions for the general dynamical properties of the system.
Ecological and evolutionary dynamics
Pea aphids in Wisconsin alfalfa fields rarely reach densities sufficient to cause crop damage due to high levels of predation and parasitism. How do predators and parasitoids act to suppress aphid populations in a persistent, stable fashion? And how does evolution counteract the effects of environmental fluctuations and predators on aphids? To address these problems, I employ experiments both in the lab and in the field, and integrate the results of the experiments using a variety of theoretical tools. As a method to explore aphid evolution, I am taking advantage of the numerous bacterial symbionts of aphids (part of the aphid extended genome) that confer heat tolerance and resistance to parasitoids and parasites. This is part of a project with Jason Harmon (NDS), Kerry Oliver (UG-Athens), and Volker Radeloff (UW-Madison).
Evolutionarily related species are likely to share many of the same traits due to their phylogenetic descent from a common ancestor. With Ted Garland (UC-Riverside) as a frequent collaborator, I develop statistical methods to investigate phylogenetic correlations of traits among species. Because the occurrence and abundance of species in ecological communities depend on their traits, community composition is also likely to show phylogenetic patterns with, for example, phylogenetically related species more likely to occur in the same communities. Thus, I am extending methods derived for comparisons of traits among species to compare the compositions of different ecological communities.
Complex population dynamics
I am involved in several projects, most of them collaborative, investigating the complex dynamics that some species exhibit. For example, Ãrni Einarsson, Vincent Jansen, Arnthor Gardarsson and I demonstrated that the extremely large but irregular fluctuations in the abundance of midges in Lake Myvatn, Iceland, could be explained by a model showing alternative dynamical states. The observed dynamics appear to shift stochastically between the two states, a high stable point and a 5-orders-of-magnitude cycle, producing dramatic and unpredictable population patterns.