The field of ecology, and from my perspective especially the fields of community and ecosystems ecology, are in a state of tremendous and exciting change. In part this is due to improved methods and theories that are revitalizing the field from an academic perspective. But this is also largely driven by changes in the motivations and goals of scientists who are increasingly interested in questions that have implications (or even applications) in solving pressing environmental issues. My goals are: to conduct research that will serve to better integrate our knowledge of ecological processes that will facilitate future understanding of environmental issues, to help train others in scientific approaches to ecology oriented at environmental issues, and to contribute to efforts at making scientific approaches to ecology more accessible to society at large.
I have been involved in three different lines of research. All are oriented at understanding how the outcomes of species interactions, involving especially predation and interspecific competition, depend on the environmental context in which they occur. My approach in general, is to use experimental and observational methods in the field to test and refine theories about underlying causal mechanisms. Almost all my work is done on aquatic (especially planktonic) organisms because they are very convenient "model systems"; however because most of my studies are closely linked to general theoretical models they can provide valuable insights into the operation of other, less tractable, systems.
Trophic and food-web interactions in ponds and lakes: One focus of my work has been to understand how the structure of communities affects the responses of entire trophic levels to environmental change. To this end, I developed and tested models of trophic interactions in food webs to explore how competition among plants is affected by herbivores that differ in their ability to feed on herbivore-resistant plants. My experiments have demonstrated that food-web structure (as described by the occurrence of specific taxa) can be qualitatively important in regulating responses of organisms to environmental change. This result is important because it violates the usual assumption that ecosystem phenomena (e.g. biomass accrual of plants and herbivores) are independent of community structure (the composition and diversity of taxa). These results are also important because they were only poorly predicted by previous models, including my own. I am currently working to refine these models to include processes that better account for the ways species from a broader regional biota sort into local communities.
Ecological genetics of competing species: In my dissertation work I documented how two species of Daphnia zooplankton segregate by habitat in stratifie. In subsequent collaboration with Alan Tessier (Mich. St. Univ.), I found a substantial amount of genetic divergence among different lake populations of both species in life-history, behavior, and in ecological traits such as the ability to exploit resources and avoid predators. There is a substantial amount of natural selection on such traits in natural that mimics, in direction and magnitude, the selection occurring in our experimental enclosures. These data indicate that the basic tradeoffs associated with ecological traits, are different in lake populations that have diverged (via natural selection in lakes with different levels of predation).
Species diversity and ecosystem productivity: Most recently I have become interested in how mechanistic approaches to community ecology can be used to understand patterns involving entire communities of interacting organisms. Most such models have focused on a small number of species (usually between 2 and 6) and I have worked to extend the results of these models to address issues of biodiversity of entire trophic levels. I have particularly focused on how ecosystem productivity can regulate the overall diversity of coexisting species of plants and herbivores in a local assemblage. I am particularly interested in determining if unimodal diversity-productivity relations might result from an interaction between the effects of interspecific competition for resources occurring within trophic levels, and the regulation of such interactions by predators between trophic levels. I have found that models based solely on resource competition are not likely explanations for observed positive inter-correlations among nutrient availabilities and overall nutrient levels in lakes. I have also documented that patterns of variation in species diversity in pond algae are closely linked to patterns of variation in density, composition, and diversity of zooplankton grazers.
The insights arising from my research on trophic interactions and, especially, from my recent work on biodiversity has led me to a different perspective on community ecology than that resulting from previous theory (as embodied in "niche-theoretic" models of species interactions). My ultimate goal is to continue to work toward developing these ideas into a more coherent theory of community ecology. I am especially excited about the work on biodiversity because environmental problems associated with biodiversity and the integrity of ecosystems are an increasingly large societal concern. In this area in particular, progress on understanding community ecology is vital from an applied perspective as well as for purely academic reasons.
Recent Publications