Phenotypic plasticity, i.e. environmentally-induced phenotypic variation, is a major means of adaptation to the (changing) environment. Phenotypic plasticity may act as a buffer to natural selection because it may reduce the fitness differences between genotypes by means of across-genotype convergence in phenotypic expression in response to the selective environment. Despite its evident ecological and evolutionary implications, phenotypic plasticity is seldom considered in community assembly studies. Community assembly results from the influence of habitat filtering (reduced range of trait values in the community relative to the regional pool: trait convergence) and limiting similarity (increased range of trait values: trait divergence). In the case of habitat filtering leading to trait convergence, phenotypic plasticity could allow more species in the community to show the “right” phenotype and thus “pass the filter”. Therefore, by being a buffer to habitat filtering, phenotypic plasticity would promote species richness in the community without altering the process of trait convergence. If phenotypic plasticity actually plays such a role, changes in the environment should modify trait distribution but not species composition or richness. We tested this hypothesis in a forest edge community where a recent invasion by a dominant alien species (Rubus constrictus) has occurred. In 24 paired quadrats across this temperate rainforest we measured 8 functional traits in all species below Rubus canopy (invaded community) and in adjacent microsites naturally free from Rubus (original community). We compared functional diversity, community structure parameters and trait distribution patterns.
Results/Conclusions
Soil nutrients were similar in both communities but there was reduced light availability in the invaded community. Using the FDis parameter we found that there was habitat filtering in the invaded community (trait convergence), while in the original community the phenotypic structure did not differ from a null model. Species richness, diversity and species composition did not differ between the two communities. This suggests that phenotypic convergence in the invaded community did not result from species sorting (i.e., selection at the species level). The latter would be verified by either reduced abundance of species with trait values distant to the community weighted mean (CWM) or increased abundance of species with trait values close to the CWM. Therefore, phenotypic plasticity might be inferred as the process underlying the observed patterns. This was further confirmed by the fact that the distance between the community mean and the CWM (an indicator of evenness in relative abundance according to species’ phenotype) was similar in both communities.