The optimal foraging theory: food selection in beavers based on tree species, size, and distance laboratory 1, ecology 201 abstract . the theory of optimal foraging and its relation to central foraging was examined by using the beaver as a model. Beaver food choice was examined by noting the species of woody vegetation, status chewed vs. Not chewed , distance from the water, and circumference of trees near a beaver pond in north carolina. Beavers avoided certain species of trees and preferred trees that were close to the water. These data suggest that beaver food choice concurs with the optimal foraging theory. introduction in this lab, we explore the theory of optimal foraging and the theory of central place foraging using beavers as the model animal.

The optimal foraging theory assumes that animals feed in a way that maximizes their net rate of energy intake per unit time pyke et al. An animal may either maximize its daily energy intake energy maximizer or minimize the time spent feeding time minimizer in order to meet minimum requirements. Herbivores commonly behave as energy maximizers belovsky 1986 and accomplish this maximizing behavior by choosing food that is of high quality and has low search and low handling time pyke et al. The central place theory is used to describe animals that collect food and store it in a fixed location in their home range, the central place jenkins 1980. The factors associated with the optimal foraging theory also apply to the central place theory.

The central place theory predicts that retrieval costs increase linearly with distance of the resource from the central place rockwood and hubbell 1987. Central place feeders are very selective when choosing food that is far from the central place since they have to spend time and energy hauling it back to the storage site schoener 1979. The main objective of this lab was to determine beaver castor canadensis food selection based on tree species, size, and distance.

Since beavers are energy maximizers jenkins 1980, belovsky 1984 and central place feeders mcginley and whitam 1985 , they make an excellent test animal for the optimal foraging theory. Beavers eat several kinds of herbaceous plants as well as the leaves, twigs, and bark of most species of woody plants that grow near water jenkins and busher 1979. By examining the trees that are chewed or not chewed in the beavers' home range, an accurate assessment of food preferences among tree species may be gained jenkins 1975. We wanted to know if beavers put the optimal foraging theory into action when selecting food. We hypothesized that the beavers in this study will choose trees that are small in circumference and closest to the water. Since the energy yield of tree species may vary significantly, we also hypothesized that beavers will show a preference for some species of trees over others regardless of circumference size or distance from the central area. The optimal foraging theory and central place theory lead us to predict that beavers, like most herbivores, will maximize their net rate of energy intake per unit time.

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In order to maximize energy, beavers will choose trees that are closest to their central place the water and require the least retrieval cost. Since beavers are trying to maximize energy, we hypothesized that they will tend to select some species of trees over others on the basis of nutritional value. This study was conducted at yates mill pond, a research area owned by the north carolina state university, on october 25 th.

Our research area was located along the edge of the pond and was approximately 100 m in length and 28 m in width. The circumference, the species, status chewed or not chewed , and distance from the water were recorded for each tree in the study area. Due to the large number of trees sampled, the work was evenly divided among four groups of students working in quadrants. We conducted a chi squared test to analyze the data with respect to beaver selection of certain tree species.

We conducted t tests to determine 1 if avoided trees were significantly farther from the water than selected trees, and 2 if chewed trees were significantly larger or smaller than not chewed trees. Mean tree distance from the water and mean tree circumference were also recorded. Overall, beavers showed a preference for certain species of trees, and their preference was based on distance from the central place. Measurements taken at the study site show that beavers avoided oaks and musclewood fig. The mean distance of 8.42 m away from the water for not chewed trees was significantly greater than the mean distance of 6.13 m for chewed trees t 3.49, d.f. The tree species that were avoided were not significantly farther from the water t.4277, d.f.