Small mammal diversity along an elevational gradient in northern Luzon, Philippines

A faunal survey conducted along an elevational gradient in Balbalasang-Balbalan National Park in northern Luzon Island, Philippines, revealed 15 species of non-flying small mammals. Thirteen, including 1 shrew and 12 murid rodents, are native species endemic to the Philippines, 7 of which are endemic to northern Luzon. Two species are non-native murid rodents that were restricted to disturbed habitats. As seen elsewhere in the Philippines, species richness was greatest in montane and mossy forest habitats at mid to high elevations. Although species-rich, the Balbalasang gradient does not include the full diversity of species known from the Central Cordillera region. Comparative data from sites elsewhere on Luzon reveal that total species richness is a function of local elevation, with more species present in areas with higher mountain peaks. These patterns reflect the fact that diversity of non-flying small mammals is concentrated in highland areas where local assemblages include species that differ in diel activity, spatial habitat use, and diet. Numerically dominant species are members of a single murid clade, and several of these are specialized predators of earthworms. Similarly structured communities in the highlands of Mindanao include species that are only distantly related to those of Luzon. Community convergence is thought to reflect the influence of similar habitat structure, food resource availability, and trophic partitioning in shaping small mammal assemblages.