Partitioning phylogenetic and functional diversity into alpha and beta components along an environmental gradient in a M editerranean rangeland

• Published in: Journal of vegetation science Vol. 24; no. 5; pp. 877 - 889
• Main Authors: Bernard‐Verdier, Maud, Flores, Olivier, Navas, Marie‐Laure, Garnier, Eric
• Format: Journal Article
• Language: English
• Published: 01.09.2013
• ISSN: 1100-9233; 1654-1103
• DOI: 10.1111/jvs.12048

Questions To what extent is the functional structure of plant communities captured by phylogenetic structure? Are some functional dimensions better represented by phylogenetic relationships? In an empirical study, we propose to test the congruence between phylogenetic and functional structure at the alpha and the beta scale along an environmental gradient. Location Causse du L arzac, southern F rance. Methods We measured species abundances and eight key functional traits in 12 plant communities distributed along a gradient of soil depth and resource availability in a M editerranean rangeland. A phylogenetic super-tree of the species was assembled, and after quantifying the degree of phylogenetic signal present in each trait, we quantified taxonomic ( TD ), phylogenetic ( PD ) and functional ( FD ) diversity both within (alpha scale) and among (beta scale) communities, taking species abundances into account. We tested for trends in diversity along the environmental gradient, and looked for congruence among different facets of diversity, both at the alpha and the beta scale. Results We found a significant phylogenetic signal for seven out of eight traits. However, when accounting for trends in taxonomic diversity (i.e. richness and evenness), PD did not capture the strong functional structure observed within and among the communities. At the alpha scale, we found an overall pattern of phylogenetic convergence of abundant species, which did not reflect the observed functional divergence. At the beta scale, despite some congruence between beta PD and beta FD for three individual traits, phylogenetic dissimilarities did not capture the overall environmental and functional sorting of species according to habitats. Conclusions We show that even when traits display a significant phylogenetic signal, PD does not capture the complex functional structure of communities in response to environmental gradients. Nevertheless, results suggest that phylogenetic relationships may partially capture differences in the beta niche of species and provide additional insights on assembly processes not captured by the set of measured functional traits. Only by accounting for patterns in taxonomic diversity were we able to disentangle the functional and evolutionary determinants of species assembly along the gradient. This study of rangeland plant communities shows how phylogenetic community structure may not capture functional structure within or among communities along an environmental gradient. We demonstrate that comparing these two facets of community structure is essential to disentangle the underlying processes of community assembly, but requires a careful taking into account of differences in species evenness among communities.