Foraging Efficiency and Habitat Switching in Competiting Sunfishes

Abstract

A series of experiments are presented which elucidate competitive interactions among 3 congeneric sunfishes (Centrarchidae). In the absence of competitors all species rank 2 habitats (vegetation, sediments) in the same order according to profitability but differ in their relative efficiencies at utilizing these habitats. The ordinal ranking of foraging efficiencies of these species in the 2 habitats permits qualitative predictions of the occurrence and order of habitat shifts as resources decline (competitive pressure increases). We present an experiment demonstrating such habitat shifts which corroborate these predictions. The patterns of habitat switching indicate that the addition of a competitor which is more effective in a given habitat can change the profitability ranking for a species to the extent that the preferred habitats are abandoned. Thus these results provide experimental evidence for the compression hypothesis as a mechanism for the development and maintenance of resource partitioning by habitat. Further, the ecological flexibility exhibited by the sunfish indicates that overlap or co—utilization of habitats can be a very dynamic process, determined by the relation between resource levels and differences in foraging efficiencies among species. The implications of these results to competition, optimal use of a patchy environment, and species abundance relations in natural lakes are discussed.