How small an island? Speciation by endemic mammals ( Apomys , Muridae) on an oceanic Philippine island

Abstract

Aim To investigate the influence of oceanic island area on speciation by small mammals, in the context of other land vertebrates. Location Mindoro Island (9,735 km 2 ), an oceanic island in the Philippines. Methods Extensive field surveys on Mindoro, followed by sequencing one mitochondrial and three nuclear genes for use in phylogenetic, population genetic and coalescent‐based analyses, and by morphometric analysis of craniodental data. Results Our analyses documented the presence on Mindoro of an endemic clade of probably four species of Apomys , subgenus Megapomys . The common ancestor likely arrived from Luzon Island across a narrow sea channel between 2.4 and 1.5 Ma; the four probable species occur allopatrically, with variation in their ranges along elevational gradients. Mindoro thus becomes the smallest oceanic island on which speciation by small mammals has been documented. Main conclusions A review of land‐living vertebrates suggests that bats and large mammals have the greatest area requirements for speciation, whereas frogs, lizards, birds and small mammals have lower and similar minimum area requirements. However, with the exception of Anolis lizards, data are scattered and limited; much research is needed to document the impact of island area on speciation. The existence of a lower limit implies that the biological processes that influence species richness do not operate equivalently along a gradient of island areas: speciation within islands may not contribute to changes in species richness below some limit, unlike colonization and extinction, which operate at all island sizes.

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