Predicting the phenotypic response of resource-competing communities to environmental change.

We formulated responses in functional traits by competitive communities to continual environmental changes, and examined the association of the trait dynamics with species richness and interspecific competition. As an aggregate measure for community properties we employed the mean community trait value as the species traits averaged over an entire community with weighting by relative species abundances. For three particular types of community, in which there was competition for abiotic resources, competition for biotic resources, or species packing on an environmental gradient, we analytically proved that the responses of the mean community trait to environmental change were determined by the total trait range in the community but were weakly associated with the strength of competition and the number of species. These results were provided with simplifying assumptions that the species trait determining the resource utility equally spaced along an univariate resource axis and the competition between species was symmetrical between pairs of competing species and within the entire community. Some numerical simulations based on stochastically-generated communities and randomly-sampled natural communities indicated that relaxation of the simplifying assumptions did not considerably violate the above conclusion. The suggested determinacy of trait dynamics with variable species richness and competition regime implies that aggregated description of communities in terms of trait distributions among composite species is relevant in predicting community responses, in terms of functional traits and ecosystem function, to environmental changes.