THE EFFECT OF HYDROLOGICAL DISTURBANCE ON THE IMPACT OF A BENTHIC INVERTEBRATE PREDATOR

Abstract

The harsh–benign model of community dynamics predicts that the impact of predation will decline as abiotic conditions become more stressful to biota. Experiments were conducted to determine whether hydrological disturbance altered the impact of an invertebrate predator in stream benthic communities. The impact of a predatory stonefly, Cosmioperla kuna, on its mayfly prey was measured in experimental stream channels receiving constant or variable flow (flooding) regimes over a one-week period. Contrary to predictions of the harsh–benign hypothesis, the impact of Cosmioperla on its two major prey taxa was either unchanged or increased by artificial floods, despite increased predator emigration from variable-flow channels. Predator impacts in variable-flow treatments were apparently strongly influenced by predator-induced prey emigration during floods. The results of this study show that nonlethal predator effects may be important during abiotic disturbance, and that it may not be reasonable to predict the impact of predation solely on the basis of the relative tolerances of predators and prey to prevailing abiotic conditions.