EFFECTS OF ARTIFICIAL BUSH CANOPIES AND ILLUMINATION ON SEED PATCH SELECTION BY HETEROMYID RODENTS

Bipedal species of seed-eating, desert, heteromyid rodents forage prim arily in open spaces while quadrupedal heteromyids forage in structura lly complex microhabitats, such as beneath bush canopies. However, bot h bipeds and quadrupeds use the latter microhabitats relatively more d uring periods of bright lunar illumination. One explanation for these patterns is that risk of predation is affected by both microhabitat ty pe and illumination, and that microhabitat use is dictated by biped-qu adruped differences in vulnerability to predators. I investigated effe cts of artificial bush canopies and illumination on seed patch selecti on by three bipedal and three quadrupedal heteromyid species in a labo ratory foraging arena. I predicted that, if predation risk affects mic rohabitat selection, rodents would forage preferentially in seed patch es characterized by less risky microhabitat and illumination condition s (i.e., in patches beneath bush canopies rather than open patches, an d in dark rather than illuminated patches). Three individual rodent sp ecies in addition to species grouped as bipeds and. quadrupeds exhibit ed the predicted preference for dark patches, but only Dipodomys merri ami preferred bush patches. No preferences were expressed for open or for illuminated patches. These results and those of previous patch cho ice experiments that used patches differing in seed distribution and s oil properties imply that both predation risk and foraging economics a ffect heteromyid patch use.