FUNCTIONAL STEREOTYPY AND FEEDING PERFORMANCE CORRELATED IN A TROPHIC SPECIALIST

If a Jack-of-all-trades is a master of none, is a Jack-of-one-trade a master of only one? Surprisingly, there have been few studies testing whether trophic specialists actually possess a limited breadth of function, and no studies relating degree of functional versatility to feeding performance on prey types that are not usually included in the specialist's diet. I tested the hypotheses that Gomphosus varius Lacepede, a coral reef fish species which feeds almost exclusively on non-elusive prey, does not adjust its prey capture mechanism and is less proficient when capturing a prey type other than its preferred resource. I used nested ANOVAs to compare high-speed videotaped jaw movements of G. varius and two coexisting confamilial trophic generalists as they captured elusive and non-elusive prey. Both of the generalists, which occasionally consume elusive prey, exhibited functional versatility when capturing elusive prey, but G. varius did not. The significantly lower capture success rate of G. varius when feeding on elusive prey, compared to the generalists, supports a causative link between G. varius' stereotypical kinematics and the virtual absence of elusive prey in its diet. Quantitative assessments of functional versatility and feeding performance are useful in analysing patterns of resource use and predicting their stability over time.