ECOLOGICAL EXPLANATION THROUGH FUNCTIONAL-MORPHOLOGY - THE FEEDING BIOLOGY OF SUNFISHES

Researchers have been using simple morphological measures as indicator s of ecological features for some time. The utility of morphological v ariables as ecological indicators depends upon our understanding of ho w the variable affects the ability of the organism to perform a partic ular task. Functional morphological analyses identify those features t hat can be directly related to behavioral performance and help to dist inguish causal functional relationships from spurious correlations. Th e behavioral abilities of the individual, in turn, shape patterns of r esource use and fitness by placing limits on the range of resources th at can be utilized and by shaping the cost/benefit curve for resource choices. Examples from research on the feeding biology of North Americ an sunfishes are discussed to illustrate how functional morphology can be used to provide explanations for differences between species in pa tterns of prey use, patterns of habitat use, ontogenetic diet switches , and population size. Trends from analyses of the evolution of fish f eeding mechanisms suggest specific functional features that are most l ikely to vary among taxa and underlie differences in feeding performan ce and diet. Included in this group of predictive variables are the or ganization of lever arms in the jaw opening and closing systems, the s ize of the mouth, and the size of muscles used in prey-crushing behavi ors. The link between morphology and ecology will be made most firmly when variables are chosen that clearly reflect the ability of the orga nism to perform relevant behaviors.