An ecoregion is defined by the WWF as a "large area of land or water that contains a geographically distinct assemblage of natural communities".
Indonesia straddles two of the Earth's biogeographical realms, large-scale divisions of the Earth's surface based on the historic and evolutionary distribution patterns of plants and animals.
The portion of Indonesia west of the Wallace Line is known as the Sundaland bioregion, which also includes Malaysia and Brunei.
When sea levels fell during the ice ages, the shallow Sunda Shelf was exposed, linking the Islands of Sundaland to the Asian continent.
New Guinea has a flora of chiefly Asian origin with many Australasian elements, and a fauna similar to that of Australia.