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

Abstract

AbstractAimTo 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 species‐specific responses, and (3) the persistence of current populations in areas that were more climatically stable over time.LocationWestern 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.ResultsWe 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 conclusionsPalaeoclimate 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.