Patterns of ecological specialization in coral reef surgeonfishes

Background/Question/Methods

The study of ecological communities is invariably linked to species’ functional niches; however, knowledge of realized functional niches is often limited. In being most specialized, those taxa that occupy the narrowest niche volumes in an n-dimensional niche hyperspace have evoked particular interest in a wide range of fields. In marine environments, where information on realized niches is inherently difficult to gather, functional traits have served as the most common predictors of ecological specialization. One prime example are herbivorous coral reef fishes, which represent a functionally important group of organisms, yet little is known about ecological specialization within this group, and most frameworks evaluating their communities rely on functional traits. Using a recently developed multidimensional framework, we compare patterns of fundamental and realized niche partitioning and ecological specialization in a diverse family of herbivorous coral reef fishes. Using an assemblage of ten species of surgeonfishes, we compare niche space occupation based on dietary preferences and foraging microhabitat selection and compare these results to morphological specialization based on eighteen morphological traits.

Results/Conclusions

We found striking differences in the patterns of niche space occupation when comparing dietary and microhabitat preferences among surgeonfish species. While morphological specialization had no predictive power with regards to dietary specialization (R² = 0.003, P = 0.87), morphological specialization showed a clear relationship with species’ microhabitat utilization during foraging (R² = 0.517, P = 0.02). Interestingly, the most morphologically specialized species appear to be microhabitat generalists, while generalized morphologies appear to favour specialization on few types of microhabitats. We then show that the specialization on open, highly accessible microhabitats may represent an important development underpinning diversification in surgeonfishes and possibly other herbivore families that has led to modern coral reef communities. Thus, our study demonstrates the need to assess realized niche space occupation in highly diverse communities, stresses the potential importance of variables other than a species’ diet, and may provide important information with regards to the evolution of modern coral reef systems and their associated fauna.