Document: DAV-3-56-25

Food preferences of keystone predators: Does a keystone predator prefer prey species with high relative abundances?

CHALCRAFT, D.R.* ¹ and W.J.RESETARITS, JR. ²

University of Illinois, Urbana, IL 61801, U.S.A. ¹
Old Dominion University, ²

Abstract:
Keystone predators were originally defined as predator species that have a disproportionately large effect on a prey community relative to their density or biomass, and more specifically, alter the outcome of competitive interactions by preferentially consuming the competitive dominants. Competitive dominants are prey species that have a stronger competitive impact than other prey species either by having a higher relative abundance and/or a higher competitive effect. Whether keystone predators preferentially consume competitive dominants because of their relatively higher density or because of factors relating to their competitive ability is unknown. We examined this question in artificial ponds using a documented keystone predator, Notopthalmus viridescens, and tadpole prey, Bufo terrestris and Rana utricularia. Previous experiments suggest that B. terrestris and R. utricularia are competitive equivalents. We experimentally manipulated the total abundance and relative abundance of B. terrestris and R. utricularia to test the hypothesis that Notopthalmus viridescens will preferentially consume the numerically dominant prey species. N. viridescens eat a constant proportion of B. terrestris regardless of total tadpole density or relative abundance. N. viridescens also eat R. utricularia tadpoles but their total effect on survivorship appears to diminish at higher tadpole densities and when R. utricularia is numerically dominant. Thus, N. viridescens consume fewer total tadpole prey when R. utricularia is numerically dominant. However, mean change in N. viridescens biomass was not affected by total density or by the relative abundance of species. These results indicate that when the competitive ability of prey species are equivalent, preference for food items by N. viridescens is not based upon relative abundances.

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This abstract is being presented at: 8:45 AM in session:
Oral Session #38: Amphibian Ecology.