PATCH UTILIZATION BY 3 SPECIES OF CHILEAN RODENTS DIFFERING IN BODY-SIZE AND MODE OF LOCOMOTION

Predation risk influences differentially the foraging decisions of rod ent species with different morphologies (body size and locomotion type ), Explanations for different foraging patterns have been derived larg ely from the behavior of heteromyid rodents, and there is a lack of in formation regarding the behavior of other rodent groups with different morphologies. Nevertheless, the explanations are thought to be applic able to other groups. In order to study the generality of hypotheses a bout the effect of morphology on foraging ecology, I investigated the foraging decisions of Chilean sigmodontine rodents (Muridae) in the la boratory, experimentally manipulating nocturnal illumination (a surrog ate of predation risk) and food distribution. Three coexisting rodent species from the Chilean matorral were compared: two quadrupeds, one w ith large body size (Phyllotis darwini) and another with small body si ze (Abrothrix olivaceus), and one small species with bipedal escape be havior (Oligoryzomys longicaudatus). The species did not differ in pat ch utilization and food consumption in response to different food dist ributions. However, there was an overall significant effect of illumin ation on food consumption. When illumination was higher, A. olivaceus and P. darwini increased food transportation to the refuge and decreas ed patch consumption and total food consumption. They also increased s ignificantly the number of trips between food patch and refuge. P. dar wini 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 se nsitivity to nocturnal illumination. Bipedality may confer less vulner ability to predation, and quadrupedal species show facultative central -place foraging, diminishing a possible greater vulnerability to poten tial risk, Former explanations for different foraging behaviors under the risk of predation may not be as general as previously assumed. Thi s study emphasizes the need to consider the particular features of the system under investigation.