Predators can strongly influence the structure and function of ecosystems through trophic cascades. Classically, trophic cascades emerge when predators eat intermediate consumers and thus have a positive, indirect effect on the base of the food chain. Recent work suggests, however, that the anti-predator behaviors of consumers can also drive trophic cascades. Consumers often reduce their foraging activity in order to minimize vulnerability to predators, but reduced foraging comes at the cost of reduced energy intake and growth. Hence, physiological (e.g., energy reserves, metabolic rate) and environmental conditions (e.g., resource availability, environmental stress) may influence how consumers balance these tradeoffs. For example, theory predicts that consumers may be more willing to accept increased predation risk while foraging when the risk of starvation is also high (i.e., low energy reserves or resources). The proposed laboratory and field experiments use a model food chain from the rocky shores of New England to examine consumer responses to predation risk. Despite considerable theory, more empirical research is necessary to better understand how ecological context shapes growth-predation risk tradeoffs in prey, which ultimately determine the strength of risk-driven trophic cascades and the impact of predators in ecological communities. Furthermore, because the stress of predation risk also affects how energy transfers up the food chain, insights from this work will improve scientific understanding of the importance of biodiversity, food web dynamics, and the use of predators in the management of natural ecosystems (e.g., Yellowstone National Park). Based at Northeastern University?s Marine Science Center (MSC), the PIs will engage students from diverse backgrounds in their research through summer internships and the many well-established K-12 outreach programs based at the MSC. Additionally, the proposed experiments will be integrated into their field-based Experimental Design in Marine Ecology course that is offered to undergraduate and graduate students at Northeastern.
Support from the National Science Foundation Doctoral Dissertation Improvement Grant (DDIG) allowed Catherine Matassa to conduct the experiments necessary to complete her dissertation research. Catherine studies the "ecology of fear," or, how predators, by scaring their prey, can have large (and sometimes surprising) effects on natural communities. Fear of predators, or "predation risk", can cause prey to increase use of refuge habitats and decrease feeding rates in order to minimize their susceptibility to predation. These anti-predator behaviors have direct consequences for prey fitness and indirectly affect the abundance and distribution of other species in the community (most notably the prey's food) and the nature and efficiency of ecological processes (transfer of energy and nutrients among trophic levels). Over the last decade, there has been a growing appreciation of the magnitude, ubiquity, and importance of these "nonconsumptive effects" of predators, so-called because predators need not consume their prey in order to have these effects. Despite an abundance of theory and meta-analyses, more empirical work (especially in the field) is necessary to identify the ecological factors and biological mechanisms that shape how prey make behavioral decisions when exposed to predation risk. Catherine's dissertation research on the rocky shores of New England provides some of the first empirical tests of these theories. She has developed a model system for investigating the effects of predation risk using a simple rocky intertidal food chain (see photographs): an invasive predatory crab (the green crab, Carcinus maenas), an intermediate consumer (the Atlantic dogwhelk, Nucella lapillus), and basal resources (barnacles, Semibalanus balanoides, and mussels, Mytilus edulis). Specifically, the DDIG from NSF allowed for the completion of two large scale field experiments and one laboratory experiment that tested predictions about the effects of temperature, habitat quality, and prey state (starvation level) on the response of prey to predation risk. The results from these experiments will be published as part of Catherineâ€™s dissertation and in peer-reviewed journals. The first parts of Catherine's doctoral research, as well as collaborative research she completed while a graduate student, have been published in top-tier, peer-reviewed ecology journals, presented at national meetings of the Benthic Ecology Society, and shared with the 100+ graduate and undergraduate students she has taught during her time as a PhD student at Northeastern University. She has involved several of these students in her research as summer interns, and has involved all of them by conducting novel "ecology of fear" experiments and using her data sets as instructional tools as part of a field-based experimental design and analysis course she teaches each fall semester. Catherine has closely mentored nine undergraduate and post-graduate students during summer internships and independent research projects, seven of whom are now enrolled in graduate school or pursuing careers in science.