 The Hindu Kush, Karakoram, Himalaya, and Patkai ranges bound the bioregion on the northwest, north, and northeast; these ranges were formed by the collision of the northward-drifting Indian subcontinent with Asia beginning 45 million years ago.The Hindu Kush, Karakoram, and Himalaya are a major biogeographic boundary between the subtropical and tropical fauna of the Indian subcontinent and the temperate-climate [[Palearctic realm.The [[Western Ghats]] and [[Sri Lanka]] are important biodiversity hotspots.