Predator Species Richness and Prey Population Variability: Effects on Diets of Benthic Stream Fishes

The feeding ecology of benthic fishes was examined in a low-gradient warm-water stream in the upper Ohio River basin to determine (1) the degree of dietary similarity among predaceous fishes; (2) the dietary response of fishes to variable prey abundance (temporal and spatial), and (3) the dietary response of fishes to varying numbers of potential interspecific competitors. Eight species of benthic fishes (Cottus bairdi, Etheostoma blennioides, E. caeruleum, E. flabellare, E. maculatum, E. variatum, E. zonale and Noturus flavus) and their associated potential benthic invertebrate prey complex were sampled at nine riffle stations along a longitudinal gradient in French Creek, New York, on seven biweekly dates during summer 1980. The distribution pattern of fishes was longitudinal; species additions occurred at successive downstream sampling stations. The density of the benthic macroinvertebrate prey complex varied more through time than space due to a midsummer peak in invertebrate populations. However, diversity varied more through space than time due to a direct correspondence with longitudinal position and with predator diversity. Predaceous benthic fishes gave no evidence of resource partitioning by prey type either during the period of lowest prey densities or because of increased numbers of potential competitors. Instead, they had the greatest diet breadth when prey densities were highest.