Effects of Artificial Bush Canopies and Illumination on Seed Patch Selection by Heteromyid Rodents

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-Bipedal species of seed-eating, desert, heteromyid rodents forage primarily in open spaces while quadrupedal heteromyids forage in structurally complex microhabitats, such as beneath bush canopies. However, both bipeds and quadrupeds use the latter microhabitats relatively more during periods of bright lunar illumination. One explanation for these patterns is that risk of predation is affected by both microhabitat type and illumination, and that microhabitat use is dictated by biped-quadruped differences in vulnerability to predators. I investigated effects of artificial bush canopies and illumination on seed patch selection by three bipedal and three quadrupedal heteromyid species in a laboratory foraging arena. I predicted that, if predation risk affects microhabitat selection, rodents would forage preferentially in seed patches characterized by less risky microhabitat and illumination conditions (i.e., in patches beneath bush canopies rather than open patches, and in dark rather than illuminated patches). Three individual rodent species in addition to species grouped as bipeds and quadrupeds exhibited the predicted preference for dark patches, but only Dipodomys merriami preferred bush patches. No preferences were expressed for open or for illuminated patches. These results and those of previous patch choice experiments that used patches differing in seed distribution and soil properties imply that both predation risk and foraging economics affect heteromyid patch use.