Optimal foraging in beaver (Castor canadensis): preference, distance, size and selectivity of trees utilized by beaver in northern lower Michigan.

Abstract

Beaver (Castor canadensis) build dams and lodges which have profound effects on local ecosystems. Water flooding and conservation due to beaver activity are important ecological concerns. Beaver forage trees from distances near and far to build dams. One would expect that such energy intensive work would place constraints on characteristics of trees chosen. In this study, we examined predictions of optimal foraging theories on beaver. We studied tree genera preference, proportion utilized, size of tree and selectivity at various distances. We collected the following data on all trees (utilized and not utilized) in our study area: 1) tree genera, 2) distance of trees from nearest open water, and 3) diameter of trees at gnawing level. The optimal foraging theories of Orian and Pearson (1979) and Schoener (1979) accurately predicted the following foraging behavior of beaver in this study. When abundant, the most nutritional genus was preferred. The proportion of trees utilized decreased at increasing distances from the shoreline. Beaver were also more selective at greater distances from the shore, as predicted by Shoener's (1979) optimal foraging model. On the other hand, we found no correlation between distance and the size of tree utilized. This contradiction may be due to the generality of optimal foraging models. Beaver, unlike other predator-prey interactions, utilize each of their prey (trees) differently, depending on size and ulimate use of the tree.