BEHAVIORAL MECHANISMS UNDERLYING VARIABLE FUNCTIONAL-RESPONSES OF BLUE CRABS, CALLINECTES-SAPIDUS FEEDING ON JUVENILE OYSTERS, CRASSOSTREA-VIRGINICA

Crab consumption rates increased significantly with increasing oyster density and temperature. Analysis of the pattern of proportional mortality with prey density indicated a displaced type II (hyperbolic) density-dependent functional response at 13-14°C, a type III (sigmoid) density-dependent functional response at 19-20°C, and a type II inversely density-dependent functional response at 26-27°C. A positive correlation between predator persistence time and attack success provides evidence for a behavioural mechanism responsible for the variable functional response. As temperature decreased, persistence time also decreased, resulting in lowered attack success and proportional mortality at low prey densities. Differences in individual crab functional responses at 19-20°C suggests that this temperature range represents a transition in feeding responses such that individual crabs may exhibit either a type II or type III functional response. Instantaneous attack rates increased 20-fold from 13-14°C to 19-20°C, and 2-fold from 19-20°C to 26-27°C; handling time estimates were constant across temperature treatments. -from Author