Complex predator-prey interactions between the rusty crayfish ( Orconectes rusticus) and invertebrate and vertebrate prey within their native range

Crayfish can have profound effects on native species where they are introduced, yet few studies have examined the role of crayfish predation on species within their native ranges. We examined interactions between predatory rusty crayfish (Orconectes rusticus) and invertebrate and vertebrate prey in Southeast Indiana, where the crayfish are a native species. We conducted multiple experiments, which included assessing the predation efficiency of rusty crayfish on salamander larvae (Eurycea cirrigea) and aquatic isopods (Lirceus fontinalis), the role of substrate in prey survival, prey responses to chemical stimuli from crayfish, and the distribution of each species in a natural stream setting. We found that crayfish almost completely eliminated isopods, but the addition of even a simple gravel substrate dramatically increased survival. Although the size of the crayfish had no effect on isopod survival, salamander larvae were more likely to survive in the presence of smaller crayfish. Neither prey species responded to chemical stimuli from crayfish, yet field observations indicated that crayfish and isopods inhabit different microhabitats within the stream. Finally, the interaction between crayfish and salamander larvae is complex with the crayfish size and the natural distribution of size classes in streams likely reducing the larval predation risk and permitting coexistence. These results indicate that although crayfish are major predators on both invertebrates and vertebrates, coexistence over evolutionary time has likely led to multiple behavioral adaptations to avoid these predators.