ABSTRACT
The island of Sri Lanka, located immediately southeast of the Indian mainland, shares the continental shelf of the India–Sri Lanka (Deccan) plate. The recognition of Sri Lanka and southern India as a globally unique biogeographic entity goes back to Alfred Russel Wallace, who identified the Ceylonese subregion of Oriental region in global zoogeography, which with much refinement of the boundary to include only moist forests have given rise to the Western Ghats and Sri Lanka biodiversity hotspot, a global conservation priority today. This delimitation recognizes the concentration of endemic assemblages of flora and fauna, currently under the threat of being lost owing directly to human impacts. Being a continental island with lesser degree of isolation compared with an oceanic one, together with its topographic and climatic heterogeneity and the eventful geological history, Sri Lanka has assembled a unique biota with an exceptionally high diversity and endemicity for its size, unlike isolated oceanic islands which usually possess highly endemic biotas depauperate in diversity. Sri Lanka experienced species colonization events from the mainland after its separation from India ~50 Ma, initially during the Oligocene followed by dispersal events in the late Miocene, Pliocene, and Pleistocene epochs during glacial periods with lowered sea level (at least five times over the last 500,000 years), followed by isolation-driven speciation during interglacial periods. The northward drifting of the Deccan plate starting deep from global south to the northern hemisphere just above the equator over the last 200 million years have given it so many different elements of biota, which took refuge in Sri Lanka especially during the volcanism of Deccan traps. Remarkable combination of 406climatic and topographic isolation mechanisms within the island have resulted in insular speciation making endemism values as high as 98% in freshwater crabs and 89% in land snails and amphibians. The remaining fragmented natural habitat patches of the island hence serve as only places for those species to strive on Earth, making this crucible of speciation in southwestern jungles of Sri Lanka a stronghold for biodiversity conservation amidst the challenges placed by the climate change.
