DETERMINANTS OF COMMUNITY STRUCTURE IN DESERT RODENTS: RISK, RESOURCE AND FORAGING BEHAVIOR.

Communities of granivorous desert rodents are structured by habitat selection and may be influenced by either predatory risk or resources. To examine these hypotheses, I manipulated illumination using lanterns, parachute canopies, or natural moonlight and resources using seeds. Foraging behavior is risk-sensitive; increased illumination reduces foraging in open areas while adding shadows to open areas using parachutes increases foraging there. Foraging behavior is also affected by resource enrichments. Differences among species in habitat selection were determined by specific abilities to detect and avoid predators. The least vulnerable species, Dipodomys deserti, foraged heavily in the open and was largely unaffected by treatments; other species of kangaroo rats and kangaroo mice also prefer the open, but responded to both risk and resource manipulations; highly vulnerable Peromyscus maniculatus was always restricted to bushes even under the most favorable circumstances; Perognathus longimembris was restricted to bushes in the absence of P. maniculatus in 1980 and was displaced from preferred microhabitats by the presence of kangaroo rats in 1981. A correlation between auditory bullar volume and use of open habitat by the various species in this community suggests that predatory risk provides an axis along which habitat segregation occurs. Predation can shape community structure by influencing foraging decisions of individuals. Desert rodents from North America and the Middle East have converged morphologically and perhaps in behavior and in community structure. Using desert rodent communities in the Great Basin Desert of U.S.A. and in the Negev Desert of Israel, I manipulated predatory risk in both communities and noted that foraging activity declines with increased predatory risk. Additional evidence suggests that predation also affects habitat selection behavior in both communities. Furthermore, differences in habitat utilization among species which promotes coexistence are related to morphological anti-predator specialization of the species. Predation appears to have shaped behavior and contributed to community structure in similar ways in both communities