APPLYING PATCH USE TO ASSESS ASPECTS OF FORAGING BEHAVIOR IN NUBIAN IBEX

Consideration of optimal patch use by animals that may face danger fro m predators and that allocate time among several activities is an exte nsion of the marginal value theorem (Brown 1988). According to the the orem, an animal should leave a food patch when its harvest rate of foo d equals the sum of its energetic and predation costs arising from for aging and its missed opportunity costs arising from foregoing other ac tivities. A technique derived from this theory involves presenting for agers with depletable food patches and measuring food density remainin g after foraging. The food density remaining is a measurement of an an imal's foraging efficiency and can be used to measure various foraging inputs. We applied the technique to Nubian ibex (Capra ibex) to obtai n information on patch use, food preference, and functional response t o food density. We used results to infer the effect of ibex on forage plants and the consequences of predatory risk. We found that (1) ibex tended to consume food from patches until the food occurred at similar densities across patches, (2) the technique can be used to determine food preference, (3) patch use by ibex led to indirect effects on comp etitive relationships between food plant species (short-term apparent competition), (4) ibex foraging effort changed with resource density, and (5) predatory risk affected patch use by ibex.