EFFECTS OF PREDATION RISK ON SPACE USE BY SMALL MAMMALS - A FIELD EXPERIMENT WITH A NEOTROPICAL RODENT

Predation is often implicated as the most important factor determining differential microhabitat use by small mammals, particularly in deser t ecosystems. This generalization, however, is based primarily on obse rvational and correlational approaches and only a few field experiment al studies. In a large scale, long-term experimental manipulation of p redators in semiarid north-central Chile, we studied the effects of ex cluding vertebrate predators on the space use of a small mammal specie s. We used three different techniques to determine space use under and away from shrubs by the diurnal, herbivorous rodent Octodon degus. Th ese included smoked tiles, fluorescent pigment tracking, and tabulatio n of numbers of runways among shrubs. Results show that O. degus used spaces away from shrubs more often, made more (and less straight) runw ays between shrubs and had smaller daily home ranges in grids where pr edators were excluded. Thus, besides the well known predator effects o f density depression and survival reduction of their prey, our study d emonstrates experimentally that prey respond behaviorally to perceived predation risks.