SPACE USE BY BEAVERS IN RELATION TO RESOURCE ABUNDANCE

Andersson's (1978; Theor. Popul. Biol. 13: 397-409) optimality model of spatial search allocation was tested for beavers fed aspen saplings in large enclosures. At initial stages of the foraging trials, when resources were uniformly distributed, foraging time per unit area, the number of saplings cut per unit area, and spatial electivity declined linearly with distance from the lodge, as predicted by the model. At subsequent stages of resource depletion there was little change in foraging time per unit area in relation to distance, which is inconsistent with the optimality model. However, the number of saplings cut per unit area and spatial electivity in sapling removal became progressively more homogeneous in relation to distance as resources were depleted, as predicted by the model. These observations suggest that beavers adjust their spatial use of resources in a manner consistent with energy-maximization objectives.