The Many Faces of Fear: Comparing the Pathways and Impacts of Nonconsumptive Predator Effects on Prey Populations

Evan L. Preisser is with University of Rhode Island, Daniel I. Bolnick is with UT Austin.Background -- Most ecological models assume that predator and prey populations interact solely through consumption: predators reduce prey densities by killing and consuming individual prey. However, predators can also reduce prey densities by forcing prey to adopt costly defensive strategies. Methodology/Principal Findings -- We build on a simple Lotka-Volterra predator-prey model to provide a heuristic tool for distinguishing between the demographic effects of consumption (consumptive effects) and of anti-predator defenses (nonconsumptive effects), and for distinguishing among the multiple mechanisms by which anti-predator defenses might reduce prey population growth rates. We illustrate these alternative pathways for nonconsumptive effects with selected empirical examples, and use a meta-analysis of published literature to estimate the mean effect size of each pathway. Overall, predation risk tends to have a much larger impact on prey foraging behavior than measures of growth, survivorship, or fecundity. Conclusions/Significance -- While our model provides a concise framework for understanding the many potential NCE pathways and their relationships to each other, our results confirm empirical research showing that prey are able to partially compensate for changes in energy income, mitigating the fitness effects of defensive changes in time budgets. Distinguishing the many facets of nonconsumptive effects raises some novel questions, and will help guide both empirical and theoretical studies of how predation risk affects prey dynamics.The authors were supported by NSF grant# DEB-0089716 to M. Turelli and J. Gillespie and the University of Texas at Austin (DIB) and by the Center for Population Biology at the University of California at Davis (ELP). This work was conducted as part of the “Does Fear Matter?” Working Group (headed by ELP and DIB) at the National Center for Ecological Analysis and Synthesis, a Center funded by NSF (grant# DEB-0072909), the University of California, and the Santa Barbara Campus. None of these sponsors or funders played any role in the design and conduct of the study, in the collection, analysis, and interpretation of the data, and in the preparation, review, or approval of the manuscript.Biological Sciences, School o