Feeding Niche Separation in a Guild of Tropical Reef Fishes (Holocentridae)

Abstract

To increase our understanding of how large numbers of similar species of reef fishes coexist, we have determined the components of feeding—niche separation among the members of a feeding guild of coral reef fishes. The seven West Indian species of shallow—water squirrelfishes (Holocentridae) comprised >99% of the nocturnally active, benthic—crustacean—feeding fishes at five sites off St. Croix, Virgin Islands. Resources utilization frequencies were determined for food and foraging habitat. Food was partitioned by taxon between the four species that consumed predominantly shrimps and the three species that ate mainly crabs. Food was secondarily partitioned by body size of prey items, particularly in the principal food category. Differences in foraging microhabitat (position within a reef zone) were as important as food differences in separating species. In all cases but one, overall feeding niche overlap was °.25 or less, with a mean value of .13. This low value contradicts statements that reef fishes are generalists with broadly overlapping resource utilization and, compared with overlap values in other guilds, suggests that the mechanism permitting great local diversity within coral reef fish guilds are not basically different from those operating in other ecosystems. The mean overlap in food among the 6 commonest species was significantly different from the mean overlaps of 50 randomly generated competition—free communities (Sale 1974), suggesting that interspecific competition has played a role in the evolution of this assemblage.