When, and how much, does fear matter? Quantitatively assessing the impact of predator intimidation of prey on community dynamics

Interactions between predators and their prey are the cornerstone of food-web ecology. Ecologists have traditionally thought of such interactions in terms of the number of prey consumed by predators. A mounting array of evidence suggests that prey are far from helpless victims, however, and that they employ a wide array of defensive strategies. The costs of these strategies can include reduced energy income, lower mating success, or increased vulnerability to other predators. Predators can thus reduce prey density both through direct consumption (density-mediated interactions, ¿DMIs¿) and through the costs arising from anti-predator strategies (trait-mediated interactions, ¿TMIs¿). The presence of TMIs can introduce nonlinearities into species interactions that profoundly affect both short-term interactions and longterm population dynamics. We will use meta-analysis to evaluate patterns of TMIs across a range of ecosystems, taxa, and as a function of predator, prey, and resource density, and to determine the relative importance of different forms of TMIs (reductions in feeding, mating opportunities, reproductive allocation, etc) in shaping predator-prey interactions. Our empirical results will be used to help develop models of predator-prey interactions incorporating both density-mediated and a range of trait-mediated effects, in turn allowing us to generate new hypotheses testable by meta-analysis. We will produce: 1) a series of articles, including one which proposes TMIappropriate experimental methodologies; 2) an article for the general public; and 3) a comprehensive database of TMI research.