Foraging in surfperches: resource partitioning or individualistic responses?

Synopsis

On Naples Reef off southern California, five sympatric species of surfperch (Embiotocidae) eat small animal prey associated with algal turf and other benthos. Although they tend to select different foods in different microhabitats, their different foraging traits are probably ‘individualistic responses’ (non-interactive or autecological species responses to resources) because the species' pairwise resource overlaps are neither uniformly small nor generally complementary. Mean overlap in both food and foraging microhabitat was significantly greater than ‘random’ as most species converged in resource use. Only two exploiters of extremes in the available spectra of prey types and microhabitats had significantly narrow overlap. Thus, resource overlaps may simply reflect similarities and differences in the species' independently evolved foraging traits, which were rendered more or less inflexible as different morphological specializations for picking, crunching, or winnowing prey. Therefore, any one species may occur about the reef to its best advantage independently of the others. Its distribution and abundance may simply reflect its tolerance of the local environment. The evidence indicates that the surfperches are not concertedly partitioning resources on Naples Reef, i.e., that the five species had not all coevolved to avoid interspecific competition in the past nor have they all mutually ‘shifted their niches’ to minimize it in the present.