Alfred R. Wallace's enduring influence on biogeographical studies of the Indo-Australian archipelago

To mark A.R. Wallace's 200th birthday, we review the direct and indirect contributions he made to our understanding of the Indo-Australian Archipelago's biogeography. He is widely known for his field research (1854–1862) and his 1863 boundary line separating the Oriental and Australasian faunal realms (between Bali and Lombok, Borneo and Sulawesi, and the Philippines and the Moluccas). Notably, though, he never accepted Huxley's ‘Wallace Line’ proposal (1868), whose northern part runs between the main Philippine islands and the Palawan Group to the west. Furthermore, in 1910, which was 3 years prior to his demise, he transferred Sulawesi's fauna to the Oriental realm. In 1924, Merrill introduced the ‘Wallacea’ transition zone. Although the label is today widely used to denote a sub-region within the Indo-Australian Archipelago between Wallace's 1863 line and Lydekker's 1896 line (first presented by Darlington in 1957), the western boundary was originally based on Huxley's line, and thus included the Philippine islands minus the Palawan group. Most biogeographers appear to be unaware of Merrill and his intention. Finally, recent attempts to define the faunal break have not led to a consensus view, despite the huge increase in primary data plus the application of modern analytical techniques. This reflects the complexities and diversity of the region's faunal distribution patterns, plus the differences in the ways that researchers choose to process their data.