Siau Island tarsier (Tarsius tumpara) is a species of tarsier from the tiny volcanic island of Siau. Its existence as a distinct taxon was predicted by the hybrid biogeographic hypothesis for Sulawesi. The rationale was that a geographic discontinuity existed between the northern tip of Sulawesi, and the population of tarsiers on Sangihe Island (the Sangihe tarsier Tarsius sangirensis), approximately 200 kilometres (120 mi) to the north. In between, lay very deep oceans and three island clusters, Biaro, Tagulandang/Ruang, and Siau. Like Sangihe Island, itself, each of these three island clusters are a part of the Sangihe Island volcanic arc. Volcanic arcs, like the Galapagos and Hawaiian Island chains, feature islands that erupt from the ocean floor. In such circumstances, islands form ind