Devil in the Details: High-resolution Dietary Analysis Contradicts a Basic Assumption of Reef-Fish Diversity Models

Abstract

Reef-fish diversity models, unlike general diversity-gradient hypotheses, assume food specialization by reef fishes is too low to influence community structure. This assumption may be an artifact of low taxonomic resolution in studies of fish diets. I performed detailed dietary analyses on adults of eight small, cryptic, diurnal fish species from the spur-and-groove habitat outside Kaneohe Bay, Oahu, Hawaii to test whether dietary specialization may facilitate high species richness in reef fish communities. Mean dietary overlap (0.179) among these fishes is similar to overlap in communities thought to be structured by fine-scale food specialization. Dietary studies with high taxonomic resolution indicate a significant decrease in food overlap among fishes as latitude decreases. These results, along with the generally recognized increase in prey diversity toward the tropics, are consistent with diversity-gradient hypotheses and suggest that food specialization allows the local coexistence of many fish species on coral reefs. Local relative abundances of reef fishes may be influenced by prey availability. The densities of five of six fish species were related to densities of important prey. Food choice and availability may influence richness and relative abundances, respectively, in reef fishes, and reef-fish communities may be structured in the same manner as other tropical communities.