Disease Ecology

Parasitism arguably represents the most widespread animal life-history strategy in nature.  Parasites also influence host traits, and can regulate host population sizes, sometimes leading to significant effects on community structure and ecosystem processes. Yet historically, the ecological roles of parasites have often been overlooked because they are not as conspicuous as free-living organisms.

A major focus of my dissertation has involved understanding how and when parasites have strong effects on communities and ecosystems. For instance, recent projects have examined the roles of parasites in food webs and secondary production within wetlands. Ongoing work aims to determine how parasites alter nutrient cycling and primary production, and in turn, how variation in nutrient availability (such as ratios of nitrogen to phosphorus) can influence disease severity.  Many of these projects involve a combination of experiments and field surveys which allow us to determine how parasites influence individual hosts and then ‘scale-up’ such measurements to ecosystems in nature.

The image at the top left shows a field site where we have extensively sampled the free-living and parasitic communities to determine the contributions of parasites to energy flow and food web interactions. The top right shows a visual representation of a wetland food web that includes parasites (image created with FoodWeb 3D). A histological section of a trematode-infected freshwater snail is shown to the bottom

left and a free-living trematode infectious stage is shown to the bottom right.

Invasion Ecology

Invasive species have become major drivers of ecosystem change, a problem that is particularly prominent in freshwaters. Understanding the effects of invasive species, however, is complicated by numerous factors in nature, such as the occurrence of multiple invaders simultaneously and concurrent environmental changes (e.g., climate, pollution, habitat alteration).

Much of my research involving invasive species has examined the factors that mediate the effects of invaders. For example, nutrient availability, habitat complexity and community structure have been found to have important roles in moderating invader impacts within expiermental wetlands. I have also used an ecosystem-level experiment to see how differences in experimental venue (e.g., laboratory enclosure, outdoor mesocosm or natural pond) alter results.

I have focused this work on two common wetland invaders: the western mosquitofish and the American bullfrog. Both species are native to the eastern United States but now occur throughout the globe. The images at left show outdoor mesocosms used to isolate species interactions, a natural wetland where we introduced invasive fish in a controlled manner, and a school of western mosquitofish.