Collaborative Research: Testing eco-evolutionary trophic cascades in aquatic ecosystems

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Changes to predator communities are occurring on a global scale. Because top predators can exert strong pressures on other species in a community, it is important to understand the consequences of their losses or gains. Will re-introduction of wolves alter current elk or moose populations? Will the loss of marine predators cause fish communities to collapse? These expectations often generate controversy. This project tests how evolutionary responses of prey to their predators might alter commonly-expected results of cascading effects within food chains. Predation, trophic cascades, and evolution are features of all natural ecosystems. Understanding how these processes interact is fundamental to interpreting past ecosystem changes and to predicting future changes. The results from this study will directly inform many of the controversies attending management of large predators. High school teachers and undergraduate students with teaching aspirations will be introduced to the ecological relevance of evolution through hands-on involvement in the research. This teacher training program will target teachers and students from traditionally underrepresented groups who work, or plan to work, in high needs schools with diverse and underprivileged students. The study of eco-evolutionary dynamics considers how ongoing evolution interacts with ecological interactions to shape population, community and ecosystem processes. Intriguing case studies suggest the effects of contemporary evolution on ecology can be large, but this area of research lacks theory that would extend its general importance. This research serves as a potential general application of the broader synthetic theory of eco-evolutionary dynamics through study of trophic cascades. It will provide an initial test of the requisite conditions of eco-evolutionary trophic cascades and quantitatively compare the magnitude and pattern of their effects to those of classical density- and behaviorally-mediated trophic cascades to understand their importance. Field surveys, manipulative experiments, and common garden experiments will be integrated to test the following predictions: 1) prey feeding traits in wild populations differ predictably in response to predator presence or absence, 2) feeding trait differences are heritable, 3) heritable differences in prey traits affect the density and species composition of prey resources, and 4) effects on prey resources cascade down food chains to influence primary producers. These conditions will be tested using recently introduced populations of Western mosquitofish inhabiting ponds with or without predatory largemouth bass. Mosquitofish are a classic system for studying both trophic cascades and contemporary evolution, and preliminary evidence supports evolutionary trade-offs between predator avoidance and resource competition. Numerous wild populations, small body size, short life span, and easy husbandry make this species well suited for the combined field and laboratory assays required for this research.