Interpopulation variation and temperature mediation of the impacts of biological invasions

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Ecologists have made substantial progress in understanding how nonnative species invade ecosystems, but have been less successful at predicting when and where such species will have significant impacts. A major challenge for prediction is context dependence, in which a nonnative species can have considerably different effects in different ecosystems and at different times. The long-term goals of my work are to i) identify environmental factors that drive spatiotemporal variation in the impact of nonnative species, and ii) integrate these factors into general predictive models. Over the next five years, I will investigate the causes of spatiotemporal variation in rates of prey consumption by nonnative freshwater animals. My lab will conduct experiments to test three overarching hypotheses. The first hypothesis predicts that individuals at the front of a spreading population exert greater impacts on food webs because such individuals are selected to be more voracious and competitive than those from the high-density core of the population. Differences in animal behavior and body size at invasion fronts have been recognized for several years, and our lab has found evidence that predation is amplified at invasion fronts. We will build on our previous work by testing the effect of time-since-invasion on the functional response (feeding efficiency) of individuals within and between populations of aquatic invasive species. Second, in these experiments we will manipulate ambient temperature to test the hypothesis that warming enhances an invasive predator's functional response such that it increases the likelihood of prey population decline. Third, we will investigate latitudinal patterns by comparing functional responses of nonnative populations of fish and crustaceans distributed across the Great Lakes-St. Lawrence River basin. We hypothesize that individuals from higher-latitude populations have stronger functional responses (owing to more rapid growth rates) than those from lower-latitude populations. Overall, this research will inform theory and aid risk assessment by identifying environmental drivers of variation in an invader's impacts across space and time. In particular, it should reveal predictive information on how the impacts of nonnative species in aquatic ecosystems are affected by climate change.