Foraging patterns of Castor canadensis at increasing distances from water at a creek and lake habitat in Michigan.

Abstract

Foraging organisms are often faced with trade-offs between the benefits and costs of obtaining certain food items. Selection is expected to favor organisms with behaviors that give them the greatest gain, energetically and in terms of reproductive fitness, with the least cost possible. These behaviors often include making choices about which types of food items to acquire, how far to travel in order to acquire them, and which size food items to bother with in relation to how much transport time and effort is required. We used the behaviors mentioned above in order to test the applicability of the optimal foraging theory on the diet composition of the beaver, Castor canadensis. We surveyed two different habitats in Michigan, each differing in tree species density and composition. We found that the beaver at these sites teneded to prey upon, or attack, one or two particular species, that they attacked larger trees further from the water, and that tree diameter made no difference when choosing any tree at any distance from the water. Conclusions are made that the species composition of the community around a beaver lodge is controlled by the foraging behavior of that beaver. Criticisms are made of the scientific quality of the theory of optimal foraging. Evolutionary consequences of the foraging behaviors, aside from the optimality model, are considered.