COLLABORATIVE RESEARCH: Factors Affecting the Nature and Strength of Indirect Effects: A Modeling and Empirical Approach

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The trophic cascade exemplifies the importance of indirect effects to the dynamics and structure of ecological communities. Classical views of trophic cascades emphasize the positive indirect effect that predators have on basal resources through their consumption of prey. Yet growing evidence indicates that we must refine our view of how different trophic levels are dynamically linked because trophic cascades can also be caused by predator-induced changes in prey behavior such as foraging activity. Despite abundant theory we have a limited empirical understanding of the factors that shape individual foraging decisions that, in turn, dictate the nature and strength of indirect effects in natural communities. Drs. Trussell and Luttbeg will use a model comparison and null hypothesis approach to explore the relative importance of density (DMIIs) and trait-mediated indirect interactions (TMIIs) to trophic cascades on rocky intertidal shores. Using a tri-trophic food chain as a model system, they will manipulate factors predicted to influence prey behavior and thus the relative strength of TMIIs in trophic cascades. The researchers will achieve these objectives by addressing the following questions: 1. How do resource levels, prey state, and predation risk shape prey foraging and growth functions? 2. How do resource levels, prey state, and predation intensity shape prey mortality functions? 3. What model best describes the short-term influence of these factors on prey foraging behavior and the strength of emergent indirect effects? 4. Do models supported by short-term data accurately predict longer-term prey behavior and the strength of emergent indirect effects? The research will make significant intellectual contributions to ecology by exploring whether attention to individual behavior improves our ability to predict the nature and strength of indirect effects in natural systems. By evaluating alternative models with empirical data, our research is novel and will build a stronger connection between ecological theory and its empirical base. Moreover, because species interactions are central to major issues in ecology, such as the use of trophic cascade theory to manage natural systems, it is critical that we understand how behavior is modified by environmental context. Broader impacts are considerable. The research will allow students at all educational levels to pursue their interests in ecology. Graduate and undergraduate training will occur during all phases of the research. As part of Northeastern?s Young Scholars Program they also will offer a summer research internship each year to a high school student from the Coastal Ocean Science Academy (COSA) that is taught by the Marine Science Center?s Outreach staff. These students are largely members of under-represented groups from Boston area public high schools. In addition to providing these students with plenty of field experience, they also will teach them how to (1) conduct basic statistical analyses, (2) write a scientific paper, and (3) develop and deliver an oral presentation on their internship experience to the Marine Science Center community.