PATCH USE BY GERBILS (GERBILLUS-ALLENBYI) IN SANDY AND ROCKY HABITATS

At a site in the Negev Desert, Israel, we measured the giving-up density of Allenby's gerbil (Gerbillus allenbyi) in experimental food patches placed along the boundary of two habitats (rock and sand) and placed in two microhabitats (bush and open). By offering equal foraging opportunities in both habitats and in both microhabitats, we assessed differences among habitats in the gerbil's perceived costs of foraging. By converting giving-up densities into quitting-harvest rates, we converted the diverse costs of foraging into a currency of energy. Quitting-harvest rates were higher in the open than bush microhabitat (owls are known to contribute a higher predation risk in the open microhabitat). Quitting-harvest rates increased sharply with distance into the rock habitat from the sand/rock habitat boundary. Quitting-harvest rates were low and constant with distance into the sand habitat. We believe that higher perceived predation risk in the rock habitat, perhaps as a result of few refuges for escaping predators, contributes to the high costs of foraging in the rock habitat and to the scarcity of gerbils in this habitat.