Trade-offs between foraging and predation risk determine habitat use in a desert baboon population

This study explored how baboons, Papio cynocephalus ursinus, in a desert population trade off foraging and predation risk in patterns of habitat use. Four hypotheses were proposed and tested; that habitats are used on the basis of (1) availability, (2) foraging rewards (following the ideal free distribution), (3) foraging rewards modified by the constraints of nocturnal predation risk (partial trade-off) or (4) foraging rewards modified by the constraints of continuous predation risk (full trade-off). Food availability in each habitat was quantified through quadrat surveys describing stem density, plant part availability and nutrient availability (protein and energy) of key plant foods per unit area. Predation risk in each habitat was evaluated using measures describing the relative threat of attack and capture by both leopards, Panthera pardus, and lions, Panthera lee; attack risk was determined on the basis of habitat visibility and predator ambush distances, while capture risk was calculated using a simple model incorporating predator and prey velocities, habitat visibility and nearest refuge distance. Patterns of baboon behaviour were assessed for adult males and females in four groups through day-follows and instantaneous sampling. The baboons did not use habitats directly in proportion to their availability in the group's ranging area (in contrast to hypothesis 1). Nor did patterns of habitat use match those expected on the basis of the ideal free distribution, either during all activities (hypothesis 2) or during feeding (hypothesis 3). Instead, the baboons spent less time feeding in the high-risk food-rich habitat but more time feeding in the low-risk relatively food-poor habitat. Baboons also preferred low-risk habitats in other activities, where during resting and grooming all habitats were avoided except the safest (where key food species were absent). These results support hypothesis 4. Deviations from these patterns by a unimale group indicate that male reproductive strategies may also play a role in habitat selection. (C) 1997 The Association for the Study of Animal Behaviour.