Generalist feeding guilds in reef fishes: Macroevolutionary sink or future source of diversity?

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 relation between the different functional traits, which relate to the 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 taxonomic, trophic and functional datasets, we analyze the functional evolution of two major radiations of reef fishes, the wrasses (Labridae) and the damselfishes (Pomacentridae). We demonstrate that the feeding habit plays 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 highlight 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.