Trait-mediated community assembly: distinguishing the signatures of biotic and abiotic filters

Conflicting hypotheses predict how traits mediate species establishment and community assembly. Traits of newly establishing individuals are predicted to converge, or be more similar to the resident, preexisting community, when the biotic or abiotic environment favors a single best phenotype, but are predicted to diverge when trait differences reduce competitive interactions. We tested these competing hypotheses using transplant seedlings in an old-field environment, and assessed the contribution of inter- and intra-specific transplant trait variation to community-level patterns. Using a soil moisture gradient and resident plant removals, we determined when traits of newly-establishing plants converge or diverge from the resident community by calculating community weighted mean traits for transplant and resident communities. We saw evidence of environmentally- and competitively-driven trait shifts that resulted in both trait convergence and divergence from the resident community, whose ...