Wallace Line

The Wallace Line is a biogeographic boundary across the Indonesian archipelago that separates predominantly Asian fauna from Australasian fauna, despite nearby islands sharing similar climates.

Wallacea: Wallacea is the biogeographic transition zone of islands between the Asian and Australian continental shelves. The line runs through this transition zone, where Asian and Australasian faunas meet.
Alfred Russel Wallace: Alfred Russel Wallace was a British naturalist who independently formulated the theory of evolution by natural selection. His observations of Indonesian wildlife established the faunal division named after him.
Bali: Bali is an Indonesian island in the Lesser Sunda chain, west of the deep Lombok Strait. Its Asian-associated fauna contrast sharply with nearby Lombok’s Australasian affinities.
Huxley Line: The Huxley Line is a proposed biogeographic boundary farther north through Southeast Asia, associated with Thomas Henry Huxley. It extends the idea of an Asian–Australasian division into a region where the faunal transition is less abrupt.
Sunda Shelf: The Sunda Shelf is the shallow continental shelf connecting mainland Southeast Asia with western Indonesian islands. When sea levels fell, land connections let many Asian animals spread across this shelf.
The Malay Archipelago: The Malay Archipelago is Alfred Russel Wallace’s 1869 account of his travels and natural-history studies in Southeast Asia. Wallace described the contrasting animal life that led him to draw the boundary.
Lombok: Lombok is an Indonesian island immediately east of Bali, separated from it by the Lombok Strait. Its fauna illustrates the abrupt shift across the line from Bali.
Weber Line: The Weber Line is a proposed boundary in Wallacea near the balance point between Asian and Australasian faunal influences. Unlike Wallace’s boundary, it describes a zone where the two faunal influences become more evenly matched.
Sahul Shelf: The Sahul Shelf is the shallow seabed connecting Australia and New Guinea. Its former land connections helped Australasian animals spread west toward the boundary.
On the Physical Geography of the Malay Archipelago: On the Physical Geography of the Malay Archipelago is Wallace’s 1863 paper on the region’s physical and biological divisions. This paper presented the geographic observations behind the line.

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