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.

Effects of Altitude on the Conservation Biogeography of Lemurs in SouthEast Madagascar

“…Although there are few data on the effects of altitude on resource abundance in montane and cloud forests in this region, trees are of smaller diameter and lower height in these habitats (Lehman, unpublished data), which likely results in lower fruit and flower abundance in these habitats. These effects of altitude on resource abundance and nestedness patterns have been documented in other mammals and regions (e.g., Cottenie and De Meester 2004;Grow et al 2013;Presley et al 2012). Grow et al (2013) noted that pygmy tarsiers (Tarsius pumilus) deal with low food abundance at high altitudes by preferentially foraging in anthropogenic forest edges, which represent habitats with high insect abundance despite being at high altitudes in central Sulawesi, Indonesia.…”

“…These effects of altitude on resource abundance and nestedness patterns have been documented in other mammals and regions (e.g., Cottenie and De Meester 2004;Grow et al 2013;Presley et al 2012). Grow et al (2013) noted that pygmy tarsiers (Tarsius pumilus) deal with low food abundance at high altitudes by preferentially foraging in anthropogenic forest edges, which represent habitats with high insect abundance despite being at high altitudes in central Sulawesi, Indonesia. Comparable results were found in a study of nestedness in bat metacommunities along altitudinal gradients in the Peruvian Andes (Presley et al 2012).…”

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

“…T. pumilus is the only species of tarsier to live above 1,500 m, and have only been found at altitudes above 1,800 m a.s.l. (Grow et al 2013;Musser and Dagosto 1987). In comparison, Dian's tarsier occurs in the same central Sulawesi region and has been studied at approximately 700 m (Merker et al 2005) up to 1,100 m (Merker 2003).…”

“…Eastern tarsiers (Genus Tarsius), found in Sulawesi and surrounding smaller islands, are the most species of all tarsiers, with five species occurring on mainland Sulawesi: Tarsius tarsier (junior synonym Tarsius spectrum); the spectral tarsier (Brandon-Jones et al 2004;Pallas 1778); Tarsius dentatus (junior synonym Tarsius dianae); Dian's tarsier (Brandon-Jones et al 2004;Niemitz et al 1991); Tarsius lariang, the Lariang tarsier (Merker and Groves 2006); T. wallacei, Wallace's tarsier ; and T. pumilus, the pygmy tarsier (Miller and Hollister 1921;Musser and Dagosto 1987). Elevation factors into the allopatric separation of the species, and pygmy tarsiers are the only highland form to occur in Sulawesi (Musser and Dagosto 1987;Grow et al 2013).…”

“…This study seeks to (1) assess the altitudinal range of pygmy tarsiers, and determine if there is overlap with lowland tarsier species; (2) describe the ranging patterns of pygmy tarsiers; and (3) compare home range sizes of pygmy tarsiers to lowland Sulawesi an tarsiers. Given that species ranges should increase as elevation increases (Stevens 1992) and tarsier food resources decline at higher altitudes (Grow et al 2013), I hypothesized that pygmy tarsiers would have a larger altitudinal range than lowland tarsiers. Further, given that an altitudinal reduction in resources has been observed in pygmy tarsier habitat (Grow et al 2013), I hypothesized that pygmy tarsiers would have relatively large home ranges.…”