Past potential habitats shed light on the biogeography of endemic tree species of the Western Ghats biodiversity hotspot, South India

Abstract

Aim To investigate how Quaternary climatic changes affected the habitats that support endemic tree species distributions in a tropical rain forest. Based on past and present predicted species distributions, we assessed (1) whether climatic conditions may have supported species survival in the same area over the studied period, (2) the effect of ecological niche specialization on speciesspecific responses, and (3) the persistence of current populations in areas that were more climatically stable over time.Location Western Ghats, Western Ghats-Sri Lanka Biodiversity Hotspot, India. MethodsWe assessed species' current bioclimatic preferences based on their occurrence data using Maxent distribution modelling. The models were projected onto past climatic conditions of the Last Glacial Maximum (LGM) and the Last Interglacial (LIG) to assess the extent of changes in species' predicted distributions through time. Further, we tested whether species' current occurrences were located non-randomly in pixels predicted to have been suitable in the past. Finally, we characterized species-specific responses in relation to plausible biogeographical scenarios.Results We identified three distinct scenarios of species' responses to past climate changes -stability, contraction and shift -depending on their bioclimatic preferences. For high-elevation species, the cool, dry LGM was less restrictive than for medium-elevation and northern lowland species. Southernmost species requiring minimal seasonality were restricted by higher LIG seasonality, and only predicted to have been present in Sri Lanka at that time. Barring these southernmost narrow endemics, past suitable habitat, within which observed current occurrences are located, were predicted for most species.Main conclusions Palaeoclimate modelling reveals the likely local persistence of most Western Ghats endemics over the last 150 kyr, a relatively recent period in this Paleogene refugium. The large spectrum of bioclimatic preferences probably arose as a result of evolutionary events prior to the Quaternary. Our results highlight the need for further studies based on molecular phylogenetics in this relatively poorly studied biodiversity hotspot.

Phylogenetic diversity in the Western Ghats biodiversity hotspot reflects environmental filtering and past niche diversification of trees

“…Historical habitat stability (Supporting Information Appendix S1: Figure S1.2d) was assessed from Last Interglacial (LIG, c . 120–140 kyr bp ), following Bose, Munoz, Ramesh, and Pélissier (). Binary maps of potential habitat models were generated for each species under present, Last Glacial Maximum (LGM; c .…”

“…21 kyr bp ) and LIG climatic conditions, and the number of species potentially occurring at all the three epochs calculated for each grid‐cell. The higher this number, the greater the number of species that could persist locally over time, thus providing an index of habitat stability (see Bose et al., for details). We note that climate stability over the Quaternary also reflects the presence of longer term refugia in the more aseasonal forests of the south (Prasad et al., ).…”

Quaternary climatic fluctuations and resulting climatically suitable areas for Eurasian owlets

“…Past climatic fluctuations have played a major role in shaping the ranges of several species, especially endemic and endangered species in the regions harboring much of today's biodiversity such as the tropics (Bose, Munoz, Ramesh, & Pélissier, ; Bueno et al, ; Carnaval & Moritz, ; Costa et al, ; Pinilla‐Buitrago, Escalante, Gutiérrez‐Velázquez, Reyes‐Castillo, & Rojas‐Soto, ; Werneck, Nogueira, Colli, Sites, & Costa, ). Regions that experience low climatic variation (climatically stable) are believed to have more endemic species (Dynesius & Jansson, ).…”

“…The LGM was the most recent driest period on Earth. The LGM characterized low average temperature, increased aridity, and a drop in sea levels (Clark & Huybers, ), leading to a change in climate, available land area, and climate‐associated changes in vegetation (Anhuf et al, ; Bose et al, ). These changes possibly altered the ranges of many species.…”

Does structural connectivity influence tree species distributions and abundance in a naturally discontinuous tropical forest formation?

“…) and that many tree species distributions can be traced back tens of thousands of years (Bose et al. ). Although shola patches are often large enough (tens to hundreds of hectares) to have self‐sustaining viable populations, most patches tend to be small, and here dispersal may have a major influence on community structure (Mohandass & Davidar ).…”