Abstract

Predation risk influences differentially the foraging decisions of rodent species with different morphologies (body size and locomotion type). Explanations for different foraging patterns have been derived largely from the behavior of heteromyid rodents, and there is a lack of information regarding the behavior of other rodent groups with different morphologies. Nevertheless, the explanations are thought to be applicable to other groups. In order to study the generality of hypotheses about the effect of morphology on foraging ecology, I investigated the foraging decisions of Chilean sigmodontine rodents (Muridae) in the laboratory, experimentally manipulating nocturnal illumination (a surrogate of predation risk) and food distribution. Three coexisting rodent species from the Chilean matorral were compared: two quadrupeds, one with large body size (Phyllotis darwini) and another with small body size (Abrothrix olivaceus), and one small species with bipedal escape behavior (Oligoryzomys longicaudatus). The species did not differ in patch utilization and food consumption in response to different food distributions. However, there was an overall significant effect of illumination on food consumption. When illumination was higher, A. olivaceus and P. darwini increased food transportation to the refuge and decreased patch consumption and total food consumption. They also increased significantly the number of trips between food patch and refuge. P. darwini showed the most cautious foraging behavior. O. longicaudatus was insensitive to different conditions of illumination. It is argued that a large body size and quadrupedal locomotion seem to confer higher sensitivity to nocturnal illumination. Bipedality may confer less vulnerability to predation, and quadrupedal species show facultative central-place foraging, diminishing a possible greater vulnerability to potential risk. Former explanations for different foraging behaviors under the risk of predation may not be as general as previously assumed. This study emphasizes the need to consider the particular features of the system under investigation.