On the advantage of being different: Nest predation and the coexistence of bird species.

A long-standing debate in ecology centers on identifying the processes that determine which species coexist in a local community. Partitioning of resources, where species differ in resource use, is often thought to reflect the primary role of competition in determining coexistence of species. However, in theory predation can favor similar patterns. This theory premises that predators increase their search intensity with increasing density of prey. One set of experiments reported here supports this premise based on predators that search for bird nests. A second set of experiments documents that predation rates are lower when nest sites are partitioned among different sites than when the same number of nests are placed in similar sites. Moreover, predation rates on experimental nests are more similar to rates on real nests when experimental nests are partitioned among different sites. These results provide support for a hypothesis that nest predation is a process that can favor coexistence of bird species that partition resources, where nest sites are the resources.