Foraging ecology of bison at the landscape and plant community levels: the applicability of energy maximization principles

Predictions of animal distribution and resource use require multi-scale consideration because animals can use different sets of selection criteria at different scales. We investigated whether patterns of distribution and resource use by free-ranging bison (Bison bison) in Prince Albert National Park, Saskatchewan, follow rules of energy maximization that hold across multiple scales. Optimality theory predicts specialization on Carex atherodes and frequency-independent selection among plant species; that is, local variation in C. atherodes biomass should not influence diet choice but only the time spent in individual patches. The summer use of resources within meadows was closely related to energy maximization principles. C. atherodes dominated the diet of bison, was selected in all meadows, and diet choice was frequency-independent among meadows in the bison range. In winter, diet was still dominated by C. atherodes, but frequency-dependent selection of Scolochloa festucacea and the relative use of Cirsium arvense were inconsistent with theoretical predictions. At a larger spatial scale, however, the probability of meadow use was not positively related to the abundance of Carex atherodes. During summer and winter, general landscape features within the daily radius of bison (2 km in summer and 1.3 km in winter), together with abiotic characteristics of meadows, had the major influence on the probability of meadow utilization. Our study suggests that bison distribution and resource use are influenced by abiotic and biotic factors which vary in importance at different spatio-temporal scales.