Phenotypic plasticity promotes species coexistence.

Ecological explanations for species coexistence assume that species' traits, and therefore the differences between species, are fixed on short timescales. However, species' traits are not fixed, but can instead change rapidly as a consequence of phenotypic plasticity. Here we use a combined experimental-theoretical approach to demonstrate that plasticity in response to interspecific competition between two aquatic plants allows for species coexistence where competitive exclusion is otherwise predicted to occur. Our results show that rapid trait changes in response to a shift in the competitive environment can promote coexistence in a way that is not captured by common measures of niche differentiation.