Similar levels of trophic and functional diversity within damselfish assemblages across Indo‐Pacific coral reefs

Abstract Understanding the forces that influence the dynamics of communities is a key challenge to undertake in changing environments. Despite recent advances in coral reef community ecology, a more comprehensive knowledge about processes (niche‐related traits and phylogenies) driving the composition of reef fish community is needed. Here, we conducted a quantitative comparison of these processes in damselfish assemblages that belong to three distinct Indo‐Pacific coral reefs differing in taxonomic composition, morphology and degree of human disturbance. We compiled a dataset of eight categorical variables to estimate functional diversity of damselfish assemblages and a second one of stable isotope ratios to evaluate isotopic diversity, a proxy of trophic diversity. Both datasets represent the eco‐functional diversity and provide insights into niche‐related traits. Indices were then computed to grasp complementary facets of this diversity: the size of multidimensional space (richness), the partitioning of niches (divergence) and the regularity in the distribution of niches (evenness) within each space. We also tested whether functional and trophic traits displayed some evolutionary niche conservatism. We found that functional richness was influenced by the number of species and functional entities (unique combination of trait values), and that the portions of the functional spaces filled by assemblages mainly overlapped. Functional divergence and evenness indices were similarly high. For trophic diversity, the isotopic richness remained equivalent, while the two other indices were of high values and did not significantly differ. Both functional and trophic traits did not display any phylogenetic conservatism. We demonstrated consistent levels of eco‐functional diversity in Indo‐Pacific coral reef damselfishes. Each assemblage hosted species whose niches were highly differentiated and evenly distributed in eco‐functional spaces of similar sizes, albeit the extent of functional space varied with the species richness. Assemblages also tended to share similar functional attributes. The inconsistent phylogenetic structures of eco‐functional traits and the similarity in diversity indices suggest that the assemblage composition of damselfishes is mainly driven by niche‐related processes rather than by phylogenetic relatedness. Our work helps to determine which mechanisms shape coral reef fish biodiversity and more particularly assemblages issued from replicated events of ecological radiation. A plain language summary is available for this article.