Invasive species can substantially alter ecological communities and ecosystem processes. I examined whether contemporary evolution (evolution that occurs on ecological timescales) and parasitism within the invaded range affect the success and impacts of an invasive species, the rusty crayfish (Orconectes rusticus). Previous research indicates that both contemporary evolution and parasitism can be important; however, community ecologists still lack a broad understanding of how these factors affect communities.
My research on contemporary evolution indicates that growth rate has diverged between the native and invaded ranges since O. rusticus were introduced to north temperate lakes. Rapid individual growth, which leads to increased reproduction in crayfish, may be selected for in invasive populations because crayfish are introduced at low densities. Faster growth in the invaded range contributes to the impacts of O. rusticus by allowing them to reach high densities and replace congeners. These findings suggest that including evolutionary potential in risk assessments may enhance our ability to predict invasion success and impacts.
My research also indicates that parasitism affects O. rusticus invasion success and impacts. I found that trematode parasites (Microphallus spp.) were associated with declines in O. rusticus population growth. I also examined the behavioral effects of Microphallus on crayfish feeding, aggression, shelter use, and predator avoidance. Infection substantially altered crayfish behavior, and had different effects on O. rusticus and its congeners. In a mesocosm experiment to test how these parasite-induced behavioral changes impact the benthic aquatic community, infected O. rusticus had a greater per-capita impact on macrophytes and macroinvertebrates than uninfected O. rusticus when fish were present, likely due to increased boldness.
Finally, I used a survey of anglers to investigate whether a change in Missouri policy to prevent crayfish introductions would have the intended consequences of protecting game fish populations and the fishing industry. I found that banning crayfish from the bait trade is unlikely to reduce angler spending, but instead could increase the revenue generated by the fishing industry by protecting game fish populations. Overall, my dissertation provides new information about the importance of contemporary evolution, parasitism, and human behavior in controlling invasion success and community composition.