The influence of fish predation in an experienced prey community

Abstract

The impact of predaceous fish on littoral macroarthropod abundances was examined during a 1-year predator density manipulation experiment in a central Texas reservoir. Six sites were selected to receive experimental units. Each site consisted of two 8-m2 plots. One plot at each site was inaccessible to fish predators, the other plot was freely accessible to fish. Fifty-four artificial substrates which simulated natural vegetation were placed in each plot to provide homogeneity in habitat structure and allow quantitative sampling of macrophyte-dwelling invertebrates. Total macroarthropod density in predator-exclusion plots exceeded densities in control plots on 10 of 12 dates examined, but this difference was significant on only 3 dates. Chironomids, the most abundant taxon in samples, were unaffected by predator manipulation. Abundances of two common species, Orthotrichia sp. (Trichoptera) and Hyalella azteca (Amphipoda), were generally enhanced by predator exclusion. Numerically minor taxa showed little or no response to the exclusion of fish. Overall, our study indicates that fish predation can reduce macroarthropod abundances, but this effect is not dramatic. Results of similar studies conducted in aquatic macroarthropod communities that have historically experienced fish predation support these findings. We suggest that experienced prey (i.e, those that naturally co-occur with fish) are likely to possess antipredator defense characteristics that greatly reduce susceptibility to predaceous fish. Therefore, removal of fish-induced mortality has a minor impact on prey survivorship.