Optimal central-place foraging by beavers, Castor canadensis, in northern lower Michigan.

Abstract

Optimal foraging theory examines predator-prey relationships with respect to energy costs and energy gains. It predicts that organisms should attempt to maximize gains and minimize costs. An area of modest research is how this theory applies to central place foragers, organisms that carry their prey back to a centrally located nest, burrow or in our case lodge. However, little research has been done on central place foraging animals which do not exceed their prey in size. Studies investigating this particular interaction have primarily focused on the beaver, presumably due to its observable and quantifiable foraging of large, discrete prey items (trees). This study examines central place foraging techniques employed by beavers at two locations (one lake and one stream) in northern lower Michigan. We found that beavers exhibited a preference for various tree genera, depending upon the location. In addition, significantly greater percentages of trees per unit area were cut closer to the shorelines. However, no correlation was found between the diameter of tree taken and distance from the shoreline within a particular genus. Finally, beavers exhibited increased selectivity in tree size as distance increased. Results were compared with previous studies and were evaluated with respect to the predictions made by optimal and central place foraging theories and their associated models.