Altitudinal Distribution and Ranging Patterns of Pygmy Tarsiers (Tarsius pumilus)

Abstract

Pygmy tarsiers (Tarsius pumilus) of central Sulawesi, Indonesia are the only species of tarsier known to live exclusively at high altitudes. This paper examines how the ranging patterns and altitudinal distribution of high-altitude pygmy tarsiers compare to those of lowland Sulawesian tarsier species, within an elevational gradient in Lore Lindu National Park. This study a) assesses the altitudinal range of pygmy tarsiers and determines the degree of overlap with lowland tarsiers; b) describes the ranging patterns of pygmy tarsiers; and c) compares the home range sizes of pygmy tarsiers to lowland tarsiers. Given that species ranges should increase as elevation increases, I hypothesized that pygmy tarsiers would have a larger altitudinal range than lowland tarsiers. Further, given that tarsier food resources decline at higher altitudes, I hypothesized that pygmy tarsiers would have relatively large home ranges. Results indicate that pygmy tarsiers within the study area are allopatrically separated from lowland tarsier species. Pygmy tarsiers were found at 2000-2300 m and do not occupy a wider elevational range than lowland tarsiers, contrary to Rapoport’s rule. Pygmy tarsier home ranges are comparable to or relatively larger than those of lowland tarsiers, although interpretation of these results is limited by a small sample size. The average home range size for the observed pygmy tarsiers was 2.0 ha, and the average nightly path length was 365.36 m. While pygmy tarsier home ranges may be larger than lowland species, nightly path length is shorter, indicating that the tarsiers do not utilize a large proportion of their home range on a nightly basis. The relatively small nightly path length of pygmy tarsiers is unexpected, given that nightly travel distances are known to increase in habitats with lower productivity. One explanation for this short nightly travel distances of pygmy tarsiers may be their biased distribution near forest edges where insects are more abundant, lessening the need to increase foraging area. A possible confounding variable for these results is seasonal change in resources, although there is no clear seasonal change in rainfall at the study site.