Behavioral indicators of predator space use: Studying species interactions through the behavior of predators

Predation has major impacts on survival and reproductive success for many species. To quantify these effects, ecologists often choose to intensively study prey populations to measure predation rates and/or estimate predator abundance. But in some cases, predation rates are less strongly related to predator abundance per se than to spatial and temporal patterns of predator space use; thus, quantifying the latter may provide meaningful surrogates of predation rates that scale up to larger areas. This is particularly true when safety for prey, especially sessile and vulnerable prey, is strongly linked to predator-free space. Our own research programs have used two general types of behavioral indicators to quantify space use by predators: giving-up densities, as a surrogate for patch quitting harvest rates, and activity density. We discuss two general mechanisms by which predator-free (or predator-poor) space is created and link these mechanisms to behavioral indicators that can be easily collected in the field. We then summarize our past work on predation on passerine nests and moth pupae to demonstrate how using behavioral indicators of space use can reveal much about the impact of a predator on its prey. We demonstrate that behavioral indicators can be used for the following: (1) leading indicators for predation rates, (2) surrogates for information otherwise difficult to obtain, (3) integrative measures of the strength of species interactions, and (4) to reveal the outcomes of ecological interactions, such as prey persistence.