Nestedness of coral reef fish across a set of fringing reefs

Nested substructure was assessed in a community of 41 species of coral reef fishes at 18 fringing reefs around the Caribbean islands of St. John and St. Thomas. Nestedness was quantified with an index, I-N, that measures the extent to which relatively species-poor assemblages are subsets of richer assemblages. I, was statistically evaluated with a delete-1 jackknife estimate of its standard error. Adults of obligate coral reef fishes, especially wrasses and damselfishes but not parrotfishes, were significantly nested. Juveniles were only weakly or not nested. Differences in nestedness and distribution and abundance of life stages across the reefs suggest that recruitment limitation largely determines community structure although predation and. perhaps, interspecific competition also contribute to community structure. As reef size and complexity were strongly correlated with species richness, a simple iterative model with density-independent colonization, stochastic and deterministic recruitment, and habitat-size dependent extinction was evaluated. The model showed that limited recruitment is sufficient to explain the observed extent of nested substructure. The model also showed that a high degree of nestedness can occur without intrinsic differences in the dispersal ability or extinction vulnerability of species. Thus, nested substructure should not be used to infer the specific processes impacting community composition.