Wallacelinjen

Wallacelinjen, known in English as the Wallace Line, is a biogeographical boundary proposed by Alfred Russel Wallace that separates the Indomalayan (Asian) and Australasian biogeographic regions in the Malay Archipelago. The line is not a physical barrier but a zoogeographic boundary reflecting historical patterns of fauna distribution.

Geographically, the line runs through the central Indonesian archipelago, roughly between Borneo and Sulawesi and between Lombok and Flores. It marks a transition zone where western faunal assemblages (Indomalayan) give way to eastern assemblages (Australasian). Later researchers identified nearby boundaries, such as Weber Line and Lydekker’s Line, which differ in exact position. The region around Sulawesi, Lombok, Timor, and adjacent islands is often described as Wallacea, a transitional zone with a mix of Asian and Australasian species.

Historically, Alfred Russel Wallace formulated the boundary during his surveys of the Malay Archipelago in the 19th century and published his observations in The Malay Archipelago (1869). The Wallace Line became a foundational concept in biogeography, illustrating how geography, marine barriers, and plate tectonics influence species distribution.

In contemporary biogeography, the line is recognized as a useful but approximate guide. It highlights the existence of a broad faunal transition zone and the complexity of dispersal in island Southeast Asia, where endemic taxa and mixed faunas reflect deep-time geological processes and, in modern times, human-mediated introductions.