The Wallace Line is a biogeographical demarcation traversing Indonesia, notably between Bali and Lombok, that marks a distinct shift in animal species despite the short distance between the islands.

Originally identified in the mid-19th century by British naturalist Alfred Russel Wallace during his travels through the Malay Archipelago, the line highlights how closely situated islands host contrasting fauna.

West of the line, on islands such as Sumatra, Java, and Borneo, the wildlife mirrors that of mainland Asia—with species including tigers, rhinoceroses, elephants, and monkeys.

To the east, on Lombok, Sulawesi, and nearby islands, fauna reflect Australasian origins, featuring marsupials, cockatoos, and the Komodo dragon.

Geological history underpins the Wallace Line’s ecological significance.

During the Pleistocene ice ages, lower sea levels connected western islands to the Asian mainland via the Sunda Shelf, enabling Asian species to migrate.

In contrast, the Lombok Strait remained deep and served as a marine barrier, preventing land-based migration to islands east of the line, which were instead colonised by Australasian fauna via over-water dispersal.

The region east of the Wallace Line, known as Wallacea, comprises islands such as Sulawesi, Lombok, Sumbawa, Flores, and Timor.

These islands were never connected to either continental shelf and host a high degree of endemic species, along with a blend of Asian and Australian-origin flora and fauna.

Wallacea remains biologically distinctive due to its geological isolation and mixed biodiversity.

Modern biogeographical research continues to explore the Wallace Line’s enduring relevance.

Recent studies attribute the asymmetrical distribution of species to tectonic-driven climate change over millions of years, which shaped differential dispersal success between Asian and Australasian species.

These findings reaffirm the line’s role in illuminating evolutionary patterns and species adaptation.

The Wallace Line remains central to contemporary conservation strategies, ecological studies, and environmental education.

It underscores the importance of preserving distinct ecological zones and acknowledges the complex interplay between geography, evolution, and biodiversity across the region.