Plant traits related to competition: how do they shape the functional diversity of communities?

The identification of functional traits critical to plant responses to the environment promotes our understanding of assembly of communities which relies on environmental filtering. However, the recent trait-community approaches mostly ignore the influence of plant-plant interactions by mainly focusing on traits related to abiotic filtering processes. The conceptual framework we propose aims to clarify how the functional diversity of communities depends on the filtering effect of competition on relevant traits. We define two types of competition-related traits: competitive effect traits reflect the changes in local resources levels due to plant activity while competitive response traits are related to plant response to these resource depletions. We then suggest that the contribution of both types of competition-related traits to functional diversity depends on the importance of competition, previously defined as the effect of competition on plant fitness relative to that of other environmental factors. Therefore, the divergence of functional diversity is predicted to be maximized at intermediate levels of competition in relation to the coexistence of species with different strategies characterized by highly contrasted values of competition-related traits.