Functional and phylogenetic consequences of plant invasion for coastal native communities.
Question: Do invasions by alien plant species with contrasting trait profiles (Arctotheca calendula, Carpobrotus spp., Conyza bonariensis and Opuntia dillenii) change the functional and phylogenetic structure of coastal plant communities? Location: Atlantic coastal habitats in Huelva (Spain). Methods: We identified species diversity and composition in 220 paired (invaded and non-invaded) plots along the coast (440 plots in total). We measured nine functional traits for every native and invader species, namely, specific leaf area (SLA), specific root length (SRL), leaf and root dry mass content (LDMC and RDMC) and carbon isotope fraction (δ13C). We calculated, at the plot scale, community means (CMs) for each trait, functional richness, Faith's phylogenetic diversity and functional and phylogenetic mean pairwise dissimilarities. Results: Three out the four species showed rather extreme trait values compared to the native flora with greater impact on invaded communities. In plots invaded by A. calendula the values of the native communities of SLA and SRL increased, while LDMC, RDMC and δ13C decreased showing CMs more similar to its functional profile. Besides, these plots showed lower functional and phylogenetic diversity in the native component of the community. In plots invaded by Carpobrotus spp. and O. dillenii the CMs values for LDMC and δ13C increased, but have little effect on the functional and phylogenetic structure of the native communities, while no differences were observed for the communities invaded by C. bonariensis (the most functionally similar to the native species). Conclusions: Our study highlights that inferring community assembly rules from the exploration of functional and phylogenetic differences between invaded and non-invaded plots is not straightforward. By considering invaders with different functional profiles, we have shown that species with different mechanisms of invasion have contrasting impacts on the community. Consequently, the effect of plant invaders differs depending on their functional distinction from the recipient community, rather than their phylogenetic origin.