Laura Gajdzik, Eric Parmentier, Loïc N. Michel, Nicolas Sturaro, Keryea Soong, Gilles Lepoint and Bruno Frédérich

Although coral reefs face drastic environmental changes, little is known about the relative importance of the ecological and evolutionary factors that shape their fish communities. Ecological factors include diet and feeding interactions (who eats whom) and represent ‘trophic diversity’. They also encompass other biological and environmental characteristics (e.g. body length, sex change or wave exposure), which together embody ‘functional diversity’. In addition, evolutionary history (or ‘phylogeny’) can affect community composition. One main hypothesis is that closely related species tend to exhibit more similar ecological traits than distant relatives. For example, the algae-herbivore relationship exhibited by two species or their association with rubble substrate may be attributed to the fact that their common ancestor already displayed those characteristics, which were thus conserved during evolution.

Aggregations of damselfishes (Dascyllus reticulatus and Pomacentrus mollucensis) in an Acropora spp. coral patch. Credit: Thomas M. DeCarlo
Aggregations of damselfishes (Dascyllus reticulatus and Pomacentrus mollucensis) in an Acropora spp. coral patch. Credit: Thomas M. DeCarlo

To estimate the influence of these two main forces, we investigated assemblages of damselfish species from different coral reefs from the Indo-Pacific. Even though these reef systems differ markedly in terms of their morphology and human disturbance, we found that the damselfish species’ assemblages showed similar levels of trophic and functional diversity across these reefs. This suggests that, within each assemblage, damselfish species consistently partitioned resources among them in an efficient and rather even manner. However, there was limited support for the idea that closely related damselfish species were more similar in functional and trophic traits than distant relatives.

Overall, we demonstrated that ecological processes seemed to have a bigger effect on the composition of damselfish assemblages than the evolutionary relatedness among species. Our study illustrates the importance of understanding the roles of ‘present’/ecological and ‘past’/evolutionary factors in shaping communities, in order to better predict how organisms living in environments submitted to acute disturbances and global climate changes will re-assemble along various trajectories of degradation.

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