Lack of behavioral response of a native crayfish to the invasive predatory swamp eel.

Invasive predators are globally pervasive and frequently drive ecological disruption, yet the mechanisms underlying extreme prey vulnerability often remain unclear. Prey that fail to recognize or appropriately respond to novel predators may experience disproportionality high mortality. In the Florida Everglades, the recent invasion of the Asian Swamp eel (Monopterus albus/javanensis) has been associated with rapid collapse of slough crayfish (Procambarus fallax), and other prey of nesting wading birds. We assessed the behaviors of slough crayfish exposed to either a common native predator, warmouth (Lepomis gulosus) or invasive Asian swamp eels. Consistent with established antipredator responses of aquatic invertebrates facing visually oriented fish predators, crayfish reduced their movement, increased spatial avoidance, and decreased feeding in the presence of warmouth. In contrast, crayfish exhibited limited or no response to swamp eels. Naïve crayfish from invaded and uninvaded wetlands showed similar responses to the different fish predators, suggesting limited recognition/responsiveness despite > 10 generations of exposure to eels. Laboratory observations of predation by swamp eels suggest that slough crayfish may face a behavioral trade-off, with native predators selecting for cryptic lifestyles while coexistence with swamp eels favors more movement and active escape responses. Our results provide an initial assessment of behavioral mechanisms that may help explain crayfish population collapses following swamp eel invasion in the Everglades, are consistent with a hypothesis of prey naiveté, and suggest that historical selective pressures and/or constraints from conflicting predation modes may represent an overlooked mechanism in studies of predator-prey dynamics involving invasive species.