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 S t. Thomas. Nestedness was quantified with an index, I-N, that measures the extent to which relatively species-poor assemblages are subsets of richer a ssemblages. I, was statistically evaluated with a delete-1 jackknife estima te of its standard error. Adults of obligate coral reef fishes, especially wrasses and damselfishes but not parrotfishes, were significantly nested. J uveniles were only weakly or not nested. Differences in nestedness and dist ribution and abundance of life stages across the reefs suggest that recruit ment limitation largely determines community structure although predation a nd. perhaps, interspecific competition also contribute to community structu re. As reef size and complexity were strongly correlated with species richn ess, a simple iterative model with density-independent colonization, stocha stic and deterministic recruitment, and habitat-size dependent extinction w as evaluated. The model showed that limited recruitment is sufficient to ex plain the observed extent of nested substructure. The model also showed tha t a high degree of nestedness can occur without intrinsic differences in th e dispersal ability or extinction vulnerability of species. Thus, nested su bstructure should not be used to infer the specific processes impacting com munity composition.