Antipredator responses of two native stream fishes to an introduced predator: Does similarity in morphology predict similarity in behavioural response?

Antipredator defences in prey species are moulded largely by predation. One general expectation is that an organism's size, shape or morphology determines the optimal set of corresponding behavioural antipredator responses. We test the hypothesis that species with similar morphology and ecology exhibit similar antipredator responses by quantifying and comparing avoidance and escape responses of two similar species, leatherside chub and redside shiner. We also examine how antipredator responses of these two species translate into mortality using experimental stream enclosures. In the presence of brown trout, redside shiner increased activity level, responded to a simulated attack sooner, quicker and had a more manoeuvrable escape than leatherside chub. Predation by brown trout decreased survival of both species, but caused higher levels of mortality in leatherside chub compared with redside shiner. Similar morphology and ecology of these two prey species does not correspond to similarity in avoidance and escape responses, and this difference has consequences for the long-term survival of these species in the presence of introduced brown trout.