Altitude and forest edges influence the density and distribution of pygmy tarsiers (Tarsius pumilus).

ABSTRACT

In this study, we examine how high-altitude ecology and anthropogenic edges relate to the density and distribution of pygmy tarsiers. Pygmy tarsiers (Tarsius pumilus) are extremely small-bodied primates (55 g) that are endemic to high-altitude forest and exhibit several differences from lowland Sulawesian tarsier species. From June to September 2010 and January to March 2012, we conducted a population census of pygmy tarsiers across multiple altitudes. Sampling took place within a 1.2 km(2) area encompassing altitudes of 2,000-2,300 m a.s.l. on Mt. Rore Katimbu in Lore Lindu National Park, central Sulawesi, Indonesia. We observed 22 individuals, with an estimated population density of 92 individuals per 100 ha. These results indicate that pygmy tarsiers live at a lower density than lowland Sulawesian tarsier species. Lower density was associated with decreased resources at higher altitudes, including decreased tree size, tree density, and insect biomass. Within the sample area, we found pygmy tarsiers in only 8 of 24 (33%) quadrats, suggesting a nonrandom distribution that probably overinflated this population density estimate. Pygmy tarsiers exhibited a clumped distribution near anthropogenic edges that were associated with increased insect abundance and biomass. Airborne insects were more abundant along forest edges than within the forest interior, and pygmy tarsiers were observed to forage along edges where there was a higher abundance of Lepidoptera and Orthoptera. Tarsiers may mitigate the decreased availability of insects at high altitudes by adjusting their ranging patterns to remain near forest edges.