PREDATION RISK AND COMPETITION AFFECT HABITAT SELECTION AND ACTIVITY OF NAMIB DESERT GERBILS

Microhabitat partitioning based on microhabitat-specific predation rates has been well documented as a mechanism of coexistence in desert rodents. In the Namib Desert, two species of rodent, a nocturnal dune hairy-footed gerbil, Gerbillurus tytonis, and a diurnal striped mouse, Rhabdomys pumilio, co-occur in a vegetated island in the dune sea. The species show a marked preference for the same microhabitat, although gerbils also inhabit a second microhabitat where predation risk is greater. We provide direct experimental evidence for the role of predation risk and both inter- and intraspecific competition in affecting foraging behavior and habitat selection of gerbils. Using two techniques (tracking and seed trays), we were able to show that gerbils decrease foraging activity in vegetated areas during periods of increased illumination (full-moon periods). Removal of a potential competitor, the striped mouse, as well as removal of conspecifics, resulted in a significant increase in gerbil foraging activity. We propose that high susceptibility to predation results in a shared preference for the safest habitat and leads to competition for limited resources.