Thesis Defense at CES on 26 March 2019 at 3:00 pm titled "A phylogenetic perceptive on the phytogeography of Western Ghats" by Divya B from CES, IISc
The Western Ghats (WG) is one of the major global biodiversity hotspots, harbouring a rich diversity of flora and fauna many of which are endemic to the WG. The current understanding of the biogeographic history of WG comes from paleo-floral records and taxonomic diversity studies, but hasn’t been explored from a phylogenetic perspective. This was the inception of my study with the main aim to understand the imprints of biogeographic history on the phylogenetic diversity (PD) of the flora of Western Ghats. I first studied the PD patterns of local deciduous forest patches (Nandi Hills, Savandurga, and Devrayanadurga) to evaluate the usefulness of PD in the Indian context. Whereas other studies have shown that PD can be decoupled from taxon richness in biodiversity hotspots, my results showed this decoupling even in regions of low diversity. I then used these tools of community phylogenetics to analyze the patterns of PD across the WG. My premise was that if the deciduous forests of the WG are indeed more recently established than the evergreen forests (as literature suggests), then evergreen PD would be high and deciduous PD would be low. My results indeed show this pattern, corroborating this hypothesis. Within the evergreen belt, I found PD patterns that corroborate the southern refuge hypothesis, with higher PD in south compared to north. I also analyzed the phylogenetic turnover between these forests and showed that whereas the deciduous and evergreen taxa have shared evolutionary histories, the evergreen taxa from different forest types have quite disparate evolutionary histories. Phylogenetic endemism (PE) analysis (analyzing ranges of clades rather than taxa) showed that most paleoendemic plots are found south of 12-degree latitude indicative of refugial regions as postulated by the southern refuge hypothesis. Toward the north and south are clusters of neo- and paleo- endemism, which indicate that clades are restricted in distribution mostly in south, but also in north, with the central WG being a region of overlap of these ranges. My study is the first to provide a phylogenetic perspective toward understanding the biogeographic history of Western Ghats. It provides a fresh line of evidence corroborating current hypotheses and uncovered many interesting patterns which need further exploration, integrating tools from both community ecology and biogeography.