Document Type

Thesis

Date of Degree Completion

Summer 1997

Degree Name

Master of Science (MS)

Department

Biology

Committee Chair

Kristina Ernest

Second Committee Member

Sheldon Johnson

Third Committee Member

Daniel D. Beck

Abstract

Optimal foraging theories relate food preference to nutrient content and nutrient availability to home range size. After synthesizing these theories, I hypothesized that the availability of preferred food plants influences the home range size of generalist herbivores. I also hypothesized that the availability of preferred foods does not affect weight gain of time-minimizing generalist herbivores, but should affect the weight gain of energy-maximizing generalist herbivores. To test these hypotheses, I studied the home ranges, weights, weight gains, food habits, and habitats of six adult female mountain beavers (Aplodontia rufa) from six separate sites where bracken fern was either present or absent. Of the 69 plant species found within at least one home range, mountain beavers showed a preference for 13 of them, including bracken fern. Mountain beavers in the bracken fern sites had significantly smaller home ranges than mountain beavers in non-bracken fern sites. Weekly weight gain and total weight did not differ between the site types. The only significant habitat difference between the two site types was the abundance of preferred plants. Bracken fern abundance accounted for most of the difference in preferred plants between the two site types. I concluded that mountain beavers act as optimal foragers by having smaller home ranges and as time-minimizers by not increasing weight gain in habitats where preferred foods are more available. This suggests that abundance of preferred foods should be considered an important habitat feature for generalist herbivores.

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