Risk of Predation and the Structure of Desert Rodent Communities

Communities of granivorous desert rodents may be influenced by either predation risk or resources. To examine the influence of these factors, I manipulated illumination, using lanterns, and resources, using seeds. Foraging behavior is responsive to changes in predation risk; increased illumination reduces foraging in open areas without cover. Foraging behavior is also affected by resource enrichments. Differences among species in habitat selection are correlated with specific abilities to detect and avoid predators. The last vulnerable species, Dipodomys deserti, foraged heavily in the open and was largely unaffected by treatments; the other species of kangaroo rats and kangaroo mice (Dipodmys merriami, Dipodomys microps, and Microdipodops pallidus) also prefer the open, but responded to both risk and resource manipulations; highly vulnerable Peromyscus maniculatus was restricted to bushes, even under the best of circumstances; Perognathus longimembris was displaced from preferred microhabitat by the presence of kangaroo rats. A correlation between auditory bullar volume and use of open habitat by the various species in this community suggests that predation risk provides an axis along which habitat segregation occurs. Predation can structure communities of mobile prey when risk differs among habitats. Animals specializing in predator avoidance and in exploitation of risky environments have reduced interactions with superior competitors; this promotes coexistence.