Parasite ecology in freshwater wetlands: Consequences for hosts, communities and ecosystems

Parasites can exert effects on multiple levels of ecological organizations, including individuals, populations, communities, and whole ecosystems. Historically, however, most research on wildlife diseases has rarely integrated across ecological scales. I used a combination of laboratory experiments and field surveys to examine how parasites in freshwater wetlands affect individual host behavior, food web structure, and ecosystem processes. First, I explored how individual behavioral responses to parasites compare to well-known behavioral responses to predators. In both the laboratory and an outdoor mesocosm experiment, I found no evidence that tadpoles alter their behavior to reduce the risk of infection prior to direct contact with parasites, despite showing strong responses to predation risk. After infection, however, tadpoles reduced activity in predictable ways based on traits of the host, the parasite, and their interaction. Such behavioral changes likely have consequences for community interactions including, competition, predation and parasite transmission. I then examined the roles of parasites and other complex life cycle organisms in a freshwater food web. I specifically asked how variation in the resolution of nodes - from taxonomic species to life stages - affects the observed role of parasites in the web. I found that parasites were prominent within the food web and were involved in 45% of the >1000 total links. Importantly, most web metrics were sensitive to node resolution, and in particular, the effects of parasites on connectance and nestedness were reversed when nodes were disaggregated. Extending these results to explore how parasites affect energy flow, I quantified the contributions of trematode parasites to the animal biomass and production in three wetland ecosystems. I found that trematode biomass exceeded that of virtually all invertebrate groups and that trematode production was comparable to many published estimated of free-living invertebrate production. Lastly, to enhance links between disease ecology and ecosystem science, I review our current understanding of how parasites can affect ecosystem structure and function, including underlying mechanisms, a review of case studies, conceptual predictions, and priorities for future research. Taken together, my findings indicate that parasites can play prominent roles in the structure and functioning of freshwater ecosystems.