Range restricted old and young lineages show the southern Western Ghats to be both a museum and a cradle of diversity for woody plants

Abstract

The Western Ghats (WG) mountain chain is a global biodiversity hotspot with high diversity and endemicity of woody plants. The latitudinal breadth of the WG offers an opportunity to determine the evolutionary drivers of latitudinal diversity patterns. We examined the spatial patterns of evolutionary diversity using complementary phylogenetic diversity and endemism measures. To examine if different regions of the WG serve as a museum or cradle of evolutionary diversity, we modelled the distribution of 470 woody plant species across the entire region.In accordance with the expectation, we found that the southern WG is both a museum and cradle of woody plant evolutionary diversity, as both old and young evolutionary lineages are restricted to the southern WG. The diversity gradient is likely driven by high geo-climatic stability in the south and phylogenetic niche conservatism for moist and aseasonal sites. This is corroborated by persistent lineage nestedness at almost all evolutionary depths (10-135 million years), and a strong correlation of evolutionary diversity with drought seasonality, precipitation and elevation. Our results highlight the global value of the WG, demonstrating, in particular, the importance of protecting the southern WG - an engine of plant diversification and persistence.

Distribution models predict climate-related range alteration or extinction of eleven threatened tropical rainforest trees in the Western Ghats

“…Precipitation variables and temperature frequently distinguish occurrence sites from background/reference sites in SDM studies (Bradie & Leung, 2017) and may be particularly significant in ecosystems moulded by precipitation gradients such as the tropical wet evergreen forests of the Southern Western Ghats (SWG) (Krishnadas et al, 2021; Pascal, 1988). Clustering of ranges of habitat specialists in SWG is likely related to past climatic stability resulting in more time for speciation, differentiation and diversification to occur (Bose et al, 2019; Cowling et al, 2015; Harrison & Noss, 2017; Joshi & Karanth, 2013) and the formation of climate refugia acting as ‘museums’ of divergent lineages (Gopal et al, 2023; Vijayakumar et al, 2016).…”

“…Environmental gradients manifest across different spatial scales with macro-scale (latitudinal) variation in temperature and precipitation seasonality and local mesoscale (elevational) variation in precipitation and temperature thresholds (Cayuela et al, 2006;Krishnadas et al, 2016;Pascal, 1988). Under these gradients, compared to the northern regions, the southern Western Ghats tree species assemblages are more diverse and specialised (Davidar et al, 2007;Gopal et al, 2023;Krishnadas et al, 2021;Page & Shanker, 2020) with higher rates of endemism and species turnover (Bose et al, 2019;Ramesh & Pascal, 1997). More than half the tree species within this zone of climatic stability are endemic to the southern region (Bossuyt et al, 2004;Gunawardene et al, 2007).…”

“…Past research on trees and woody plants in the SWG has attested the region's phylogenetic importance (Bose et al, 2019;Chitale et al, 2014;Gopal et al, 2023;Joshi & Karanth, 2013) and documented patterns in plant community composition and diversity across environmental gradients (Davidar et al, 2007;Krishnadas et al, 2016Krishnadas et al, , 2021Page & Shanker, 2020;Pascal, 1988;Vijayakumar et al, 2016). The role of the SWG as climate refugia under future climate change and anticipated changes in species distributions are as yet poorly documented.…”

“…Such migrations and shifts (contraction/expansion) in species distribution patterns (Roberts & Hamann, 2016) may occur under varying velocities (Loarie et al, 2009) towards associated suitable or stable climate refugia characterised by low climatic fluctuations (Gavin et al, 2014; Stebbins & Major, 1965). Climate refugia act as cradles for endemism and species diversification (Gopal et al, 2023; Harrison & Noss, 2017) and understanding how species occurrence and distribution patterns change with environmental and climate gradients can throw light on future adaptation or extirpation scenarios in these regions (Bonachela et al, 2021; Neilson et al, 2005).…”

Idiosyncrasies unveiled: examining the pace, patterns and predictors of biotic diversification in peninsular India

“…It is also likely that the biomes and ranges that comprise the old lineages constitute museums of biodiversity, whereas the ones composed of young lineages constitute cradles of biodiversity. A recent study on endemic woody plants suggests that the Western Ghats is both a museum and a cradle of diversity(Gopal et al 2023). Given many endemic lineages (e.g.…”