Contrasting patterns of phylogenetic diversity across climatic zones of Western Ghats: A biodiversity hotspot in peninsular India
Résumé
This study attempts to understand the biogeographic history of the Western Ghats forests byinvestigating decoupling between phylogenetic and taxonomic diversity. We specifically test whether thedeciduous forests have been recently established, whether the southern region was a refuge, and whetherthe deciduous and evergreen forest species have disparate evolutionary histories. We used speciescomposition data from 23 forest types along the Western Ghats for all woody angiosperms above 10‐cmdiameter at breast height. Forests were broadly grouped as either evergreen or deciduous. Meanphylogenetic distances corrected for species richness and mean phylogenetic beta diversity corrected forshared species were assessed using z‐scores from null distributions. Null distributions were generated byrandomizing the species relationships on the phylogeny. We found that all evergreen forests showed agreater phylogenetic diversity as compared with null expectations. Deciduous forests showed the inversepattern. Within the evergreen belt, there was a decreasing phylogenetic diversity from south to north, aspredicted by the southern refuge hypothesis. The phylogenetic beta diversity across evergreen–deciduousforests was lesser than the null expectation, whereas it was much higher across forests within theevergreen belt. This study provides the first phylogenetic evidence for the antiquity of evergreen forests aswell as the southern refuge hypothesis in the Western Ghats. The deciduous forests species have sharedevolutionary histories with the evergreen forest species, suggesting multiple shifts between evergreen anddeciduous states through the lineages. Conversely, the evergreen species exhibited a disparateevolutionary history across these forests, possibly owing to sharper ecological or climatic gradients.