2.6 Phylogenetic analysis
Standardized effect size measure of mean nearest taxon distance (ses.MNTD) was used to quantify phylogenetic relationships between closely related taxa (Webb et al., 2002). Negative ses.MNTD value ( < 0) suggests that species are more closely related than expected by chance (clustering), whereas positive value ( > 0) indicates that species are less closely related than expected by chance (over dispersion). The calculation was implemented in the R environment (http://www.r-project.org) with the Picante package using the null model ‘taxa.labels’ (999 randomization) (Kembel et al., 2010).