Global patterns in the divergence between phylogenetic diversity and species richness in terrestrial birds

Abstract

Aim The conservation value of sites is often based on species richness (SR).However, metrics of phylogenetic diversity (PD) reflect a community’s evolu-tionary potential and reveal the potential for additional conservation valueabove that based purely on SR. Although PD is typically correlated with SR,localized differences in this relationship have been found in different taxa.Here, we explore geographical variation in global avian PD. We identify wherePD is higher or lower than expected (from SR) and explore correlates of thosedifferences, to find communities with high irreplaceability, in terms of theuniqueness of evolutionary histories.Location Global terrestrial.Methods Using comprehensive avian phylogenies and global distributionaldata for all extant birds, we calculated SR and Faith’s PD, a widely appliedmeasure of community PD, across the terrestrial world. We modelled the rela-tionship between avian PD for terrestrial birds and its potential environmentalcorrelates. Analyses were conducted at a global scale and also for individualbiogeographical realms. Potential explanatory variables of PD included SR,long-term climate stability, climatic diversity (using altitudinal range as aproxy), habitat diversity and proximity to neighbouring realms.Results We identified areas of high and low relative PD (rPD; PD relative tothat expected given SR). Areas of high rPD were associated with deserts andislands, while areas of low rPD were associated with historical glaciation. Ourresults suggest that rPD is correlated with different environmental variables indifferent parts of the world.Main conclusions There is geographical variation in avian rPD, much ofwhich can be explained by putative drivers. However, the importance of thesedrivers shows pronounced regional variation. Moreover, the variation in avianrPD differs substantially from patterns found for mammals and amphibians.We suggest that PD adds additional insights about the irreplaceability of com-munities to conventional metrics of biodiversity based on SR, and could beusefully included in assessments of site valuation and prioritization