Contrasting patterns of phylogenetic diversity across climatic zones of Western Ghats, a biodiversity hotspot in peninsular India
2020
This study attempts to understand the biogeographic history of the Western Ghats forests by
investigating decoupling between phylogenetic and taxonomic diversity. We specifically test whether the
deciduous forests have been recently established, whether the southern region was a refuge, and whether
the deciduous and evergreen forest species have disparate evolutionary histories. We used species
composition data from 23 forest types along the Western Ghats for all woody angiosperms above 10‐cm
diameter at breast height. Forests were broadly grouped as either evergreen or deciduous. Mean
phylogenetic distances corrected for species richness and mean phylogenetic beta diversity corrected for
shared species were assessed using z‐scores from null distributions. Null distributions were generated by
randomizing the species relationships on the phylogeny. We found that all evergreen forests showed a
greater phylogenetic diversity as compared with null expectations. Deciduous forests showed the inverse
pattern. Within the evergreen belt, there was a decreasing phylogenetic diversity from south to north, as
predicted by the southern refuge hypothesis. The phylogenetic beta diversity across evergreen–deciduous
forests was lesser than the null expectation, whereas it was much higher across forests within the
evergreen belt. This study provides the first phylogenetic evidence for the antiquity of evergreen forests as
well as the southern refuge hypothesis in the Western Ghats. The deciduous forests species have shared
evolutionary histories with the evergreen forest species, suggesting multiple shifts between evergreen and
deciduous states through the lineages. Conversely, the evergreen species exhibited a disparate
evolutionary history across these forests, possibly owing to sharper ecological or climatic gradients.
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