Biodiversity surveys in the 1960s and 1990s on Camiguin Island, a geologically young, volcanically active oceanic island surrounded by deep water, have demonstrated the presence of 24 species of land mammals. Three species (one insectivore and two rodents) are not native to the Philippines, but all others (one insectivore, 12 bats, one monkey, four rodents, two small carnivores, and one ungulate) are indigenous. Among those captured in the 1990s were two previously unknown species of murid rodents in the genera Apomys and Bullimus that are endemic to Camiguin. The discovery of two new species on such a small island (ca. 265 km2) is remarkable; Camiguin is currently the smallest island in the Philippines known to have unique species of mammals. Total species richness of nonvolant mammals on Camiguin is low, but relative to islands that were once part of Pleistocene Greater Mindanao, Camiguin is not depauperate. However, its fauna is not ecologically balanced in the same way as the faunas of the islands that were part of Greater Mindanao: ground-living shrews (Crocidura) and rodents (Apomys, Bullimus, Crunomys, and Rattus) from lowland forest, along with some large mammals (Macaca, Paradoxurus, and Sus) are well represented on Camiguin, but all the arboreal small mammals that characterize lowland forest on Mindanao (Sundasciurus, Exilisciurus, Cynocephalus, and Tarsius), ground-living small mammals from montane habitats (Urogale, Podogymnura, Batomys, Limnomys, and Tarsomys), and one large mammal (Cervus) are absent. Additionally, at least two genera of fruit bats (Haplonycteris and Megaerops) that are fairly common in lowland rain forests on Mindanao are absent on Camiguin. The presence of some nonvolant mammals demonstrates that dispersal across the deep but narrow intervening channel takes place, but the presence of two species endemic to Camiguin and the absence of other species that are present on nearby Mindanao implies that dispersal probably is rare. The Asian house shrew (Suncus murinus) was remarkably abundant in primary forest at high elevation; this species has also been found to be abundant in montane primary forest on Negros Island, which also has low total species richness. Species richness of small nonflying mammals was greatest at fairly high elevation.
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