Beavers (Castor canadensis) are important as ecosystem engineers and are useful model organisms for testing central-place foraging theory. Much previous work has done this in controlled situations, whereas here we tested predictions in a complex natural habitat by collecting data on beaver-cut and uncut trees in sites at various distances from an isolated beaver lodge on a large reservoir. The most basic theoretical predictions are that selectivity of predators should increase with distance from the central place and that preferred prey size should increase with distance. Consistent with the first prediction, beavers were more selective for preferred tree species when foraging far from shore or at sites some distance from their lodge than when near the shore or at sites near their lodge. Consistent with both predictions, beavers were more selective for particular sizes of trees and selected larger sizes of trees as distance from the shore increased. Overall, beavers showed a preference for intermediate tree sizes, avoiding both very large and very small trees, but as distance from shore increased, beavers cut fewer trees from the smaller end of this size range and more from the upper end in such a manner as to increase both selectivity and mean size. Similarly and within this same size range, as distance from the lodge through the water increased, beavers cut larger trees at greater distances due to reduced cutting of small trees and increased cutting of larger ones. In this case, however, overall selectivity did not increase, just an increase in the size selected. Overall, then, our study shows that central-place foraging theory can predict the behavior of beavers foraging in a complex natural landscape, and the patterns observed have implications for how beavers might influence tree species composition in forests.
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Vol. 162 • No. 1