Individuals interact with others of their kind, and with other species. In some cases just a few interactions can explain a lot about population dynamics and the structure of communities. This leads to simple explanations of observed patterns. In other cases population dynamics depend on the mixed effects of many processes, biotic and abiotic. I am interested in both cases. My work is founded in natural field settings and mostly involves parasitoid wasps and the species with which they interact. I use observational studies, manipulative experiments, population genetics, modeling, and analyses of long-term survey data.

The research system in this talk is a plant-insect community inhabiting 4000 habitat patches. Starting with individual behavior, I ask why a parasitoid uses only 1/3 of an available, yet limited, resource? How can this behavioral restraint be maintained? Next, I consider multitrophic indirect interactions, going as far as the fourth trophic level. I find, for example, that plant chemical defense and plant volatile cues determine the structure of the community. Moving to population dynamics, in classic textbook descriptions, host-parasitoid dynamics have density dependent oscillations. In fact, density dependence is often not evident. I will show, for a butterfly and two host-specific parasitoids, what factors actually control their short-term population dynamics. Finally, using a 25-year survey of six interacting species, I test the ability of direct and indirect interactions to explain large-area and long-term trends. While multiple interactions are needed to understand many short term and local phenomena, only a few are needed to explain large scale community dynamics. Weather plays a big part, and its influence is increasing.