Trait-based ecology, trait-free ecology, and in between

Trait-based ecology has become a popular phrase. But all species have traits, and their contributions to ecological processes are governed by those traits. So then, is not all ecology trait-based? Actually, there do exist areas of ecology that are consciously trait-free, such as neutral theory and species abundance distributions. But much of ecology could be considered actually or potentially trait-based. A spectrum is described, from trait-free through trait-implicit and trait-explicit to trait-centric. Trait-centric ecology includes positioning ecological strategies along trait dimensions, with a view to inferring commonalities and to generalizing from species studied in more detail. Trait-explicit includes physiological and functional ecology, and areas of community ecology and ecosystem function that invoke traits. Trait-implicit topics are those where it is important that species are different, but formulations did not initially characterize the differences via traits. Subsequently, strands within these trait-implicit topics have often moved towards making use of species traits, so the boundary with trait-explicit is permeable. Trait-based ecology is productive because of the dialogue between understanding processes in detail, via traits that relate most closely, and generalizing across many species, via traits that can be compared widely. An enduring key question for trait-based ecology is which traits for which processes.