We used taxonomic classification of WoRMS as a proxy to
phylogenetic relatedness between taxa. Phylogenetic beta diversity
(PBD) measures the evolutionary dissimilarity among communities.
A common PBD metric, UniFrac, measures the proportion of
evolutionary history unique to each community (Lozupone et al.,
2011). It is calculated as the total branch length unique to each
community relative to the total branch length linking all species in
both communities. PBD can result from two sources: (1) difference
in taxon richness between the two communities, and (2) true
phylogenetic turnover of taxa. We hereby used an algorithm that
decomposes the total PBD into the two independent components
(Leprieur et al., 2012), and use the turnover component to express
phylogenetic dissimilarity between locations. For PBD the same
stratified community matrix was used as for compositional relatedness.
The resulting dissimilarity matrix was visualized with
NMDS ordination, where communities with common evolutionary
history were grouped together, and phylogenetically distantly
related communities were more separated on a two-dimensional
plot.