Copyright 1994 by the Ecological Society of America.
Published in Ecology, Vol. 75, No. 2 (March 1994).


In northern Wisconsin lakes, the introduced crayfish Orconectes rusticus is replacing O. propinquus, a previous invader, and O. virilis, a native crayfish. Herein, we explore how fish predation and competition interact to drive this change in crayfish species composition. In outside pools, we conducted selective predation experiments exposing crayfish to largemouth bass, Micropterus salmoides, to quantify patterns of crayfish vulnerability. To determine how interactions among crayfish influence susceptibility, we quantified shelter use and behavioral interactions among crayfish in aquaria and outside pools. Based on our results, largemouth bass predation modifies the outcome of interference competition among the three crayfishes and, in turn, competitive interactions among the crayfishes influence susceptibility to fish predation. We predict that O. virilis should suffer high mortality to fish predation in the presence, rather than in the absence, of the two invading species. Our results support the hypothesis that, in areas of sympatry where predators are selective and prey species compete, predation and competition interact to determine community structure.



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