干旱区生态环境知识资源中心

Consideration of optimal patch use by animals that may face danger from predators and that allocate time among several activities is an extension of the marginal value theorem (Brown 1988). According to the theorem, an animal should leave a food patch when its harvest rate of food equals the sum of its energetic and predation costs arising from foraging and its missed opportunity costs arising from foregoing other activities. A technique derived from this theory involves presenting foragers with depletable food patches and measuring food density remaining after foraging. The food density remaining is a measurement of an animal’s foraging efficiency and can be used to measure various foraging inputs. We applied the technique to Nubian ibex (Capra ibex) to obtain information on patch use, food preference, and functional response to 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 competitive 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.