Spatial patterns of phylogenetic diversity and endemism in the Western Ghats, India: a case study using ancient predatory arthropods

Abstract

Aim: To study patterns of phylogenetic diversity, endemism and turnover in a community of ancient arthropods across a biodiversity hotspot. Our specific aims were to understand diversity gradients, identify hotspots of endemism and conservation importance, and highlight poorly-studied areas with unique biodiversity. Location: The Western Ghats (WG), India. Methods: We compiled a location data-set for 19 scolopendrid centipedes species which was used to predict areas of habitat suitability using bioclimatic and geomorphological variables in Maxent. We used predicted distributions and time-calibrated species phylogeny to calculate taxonomic and phylogenetic indices of diversity, endemism and turnover. Results: We observed a decreasing gradient in Taxonomic and Phylogenetic Diversity (TD/PD) from the southern to northern WG and high Phylogenetic Endemism (PE) in the southern and northern WG. Southern WG had the highest diversity and was represented by lineages with long branch lengths and short ranges as observed from Relative Phylogenetic Diversity/Endemism (RPD and RPE). Despite having low PD, the northern WG had high values of PE represented by distinct lineages as inferred from RPE. Sites across the Palghat Gap grouped separately in comparisons of species turnover along the WG. Main conclusions: Our findings support expectations from the latitudinal diversity gradient in the WG and the southern WG refuge hypotheses. The high diversity and endemism along with the presence of ancient lineages in the southern WG is consistent with in-situ speciation. Climatic differences or dispersal barriers might have retained this diversity locally. High phylogenetic endemism in lateritic plateaus of the northern WG, albeit with low phylogenetic diversity, indicates the presence of distinct evolutionary lineages that might be adapted to life in these landscapes characterized by poor soil conditions and seasonal ephemeral habitats. Our results from soil arthropods highlight the need to use phylogeny and distribution data while assessing diversity and endemism patterns in the WG.