Abstract
canum) and mealworm larvae (Tenebrio molitor) were introduced to the stream by conveyor belt and the ratio of prey species was changed over an 11 d period from 0:1-5:1. Two of five individuals appeared to switch to the most abundant prey species. Preference values based on a model of switching (Murdoch, 1969) differed among individuals and varied as much as five-fold among 5 min intervals. In some individuals diet preferences reversed during 30 min bouts; shortterm changes in feeding preference were not generally predictive of longer-term trends. Individual differences were detected in the expression of negative bias toward tent caterpillars. Some effects of exposure to relatively unpalatable prey appeared to extend over at least a 24 d period. Studies of foraging variability should contribute to an understanding of the role of switching in stabilizing prey communities and to the successful application of optimal foraging theory to stream fishes.
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