Diversification and functional evolution in reef fishes: The generalist feeding guild is not an evolutionary sink

Reef fishes have diversified into thousands of species that fill various types of ecological niches, contributing to the tremendous biodiversity of reef ecosystems. Yet, the dynamics of this diversity remain understudied, especially the evolutionary relationships between the different functional traits, which reflect life strategies and ecosystem roles of organisms. Here, we explore how one functional trait, the feeding habit, impacts the dynamics of species diversification and functional evolution. Using comparative phylogenetic methods in conjunction with trophic and functional datasets, we analyse the functional evolution of two major radiations of reef fishes, the wrasses (Labridae) and the damselfishes (Pomacentridae). We demonstrate that feeding habits play a key role in the evolution of the rest of functional diversity. The nature and the diversity of functional roles hosted by fish in reef ecosystems are tightly linked to their feeding attributes. Counter to a simple prediction of ecological opportunism, we found that “generalist” feeding guilds (i.e. those composed of species feeding on food sources from the whole bentho-pelagic compartment) do not show higher rates of functional diversification and do not necessarily display higher levels of functional diversity. Furthermore, in contrast to recent macroevolutionary studies on mammals and birds, we argue that these “generalist” guilds of fishes represent the basis of future diversity and cannot be considered as evolutionary sinks or as "dead-ends". These findings clearly re-define our view on the ecological and evolutionary roles played by generalist feeding guilds