THE INTERACTION BETWEEN ANTIPREDATOR BEHAVIOR AND ANTIPREDATOR MORPHOLOGY - EXPERIMENTS WITH FATHEAD MINNOWS AND BROOK STICKLEBACKS

Prey species have two fundamental strategies for reducing their probab ility of being killed by a predator: behavioural modification and morp hological defenses. It is hypothesized that prey species which possess morphological defenses should exhibit less behavioural modification i n response to predation risk than species lacking such defenses. Exper iments were conducted to examine behavioural modification by armoured (brook sticklebacks, Culea inconstans) and unarmoured (fathead minnows , Pimephales promelas) prey species foraging in the presence of a pred ator (yellow perch, Perca flavescens). Two experiments measured habita t avoidance and reactive distance to an approaching predator. The resu lts of these experiments were consistent with the hypothesis. Compared with fathead minnows, brook sticklebacks exhibited relatively little behavioural modification in response to the presence of a predator, bo th in terms of avoiding dangerous areas and in their reactive distance to an approaching predator. Sticklebacks, however, graded their react ive distance to an approaching predator in relation to both their body size and group size. These data suggest that the morphology of brook sticklebacks and their behavioural sensitivity to predation risk may a llow them to efficiently exploit habitats that contain predators.