The Theory of Island Biogeography (TIB) predicts how area and isolation, through colonization and extinction dynamics, influence the equilibrium species richness on insular habitats, such as ponds, forest fragments or coral reefs. However, the TIB remains silent about the body-size distribution within species assemblages, a determinant aspect of community structure for ecosystem functioning. To fill this gap, we develop models of island biogeography that predict body-size distribution as a function of habitat area and isolation. These models integrate species dispersal potential and trophic position, which are known to scale with body-size and to influence species spatial dynamics. We compare the model predictions to the body-size distribution of piscivorous and herbivorous fish found in tropical reefs, using a published database of 991 tropical reef-associated fish species and their occurence in 134 locations worldwide.
Results/Conclusions
We find that isolated reefs have a higher proportion of large-sized species, with fewer species of extreme size than connected ones. Interestingly, reef area influences the body-size distribution of piscivorous reef fish assemblages but have little effect on herbivorous ones. We conclude that the scaling of trophic position with body size explains the global distribution of body-size observed in piscivorous fish assemblages, while the relationship between size and dispersal potential drives the global distribution of herbivorous reef-associated fishes. The integration of functional ecology to island biogeography models presented in this study is broadly applicable to any functional trait and provides a general probabilistic approach to study the scaling of trait distribution with area and isolation. This framework open new perspectives in the fields of macroecology, functional ecology and ecosystem management since it highlights the potential impact of habitat destruction and fragmentation on the functional reorganization of species assemblages.