Traits are functional
Trait-based ecology relates individual fitness to ecosystem functioning, an integrated approach that beautifully surpasses traditional discrete levels of organization of life from organs to biomes. One promise of functional ecology is to predict ecosystem functions from values of traits involved directly or indirectly on such functions.
Functional traits are defined as traits that affect individual fitness (Violle et al. 2007), and represent ecological strategies that determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties (Pérez-Harguindeguy et al. 2013). I argue that all traits are potentially linked to fitness. To acknowledge the potential link of all traits to fitness considers(i) the integration of the phenotype, (ii) the spatio-temporal variation of environmental pressures, and (iii)the genotype by environment interaction effect on the phenotype. Here I develop reasons that support the case that all traits are related to fitness, and thus are functional by definition.