Abundance and community structure of Mentawai primates in the Peleonan forest, north Siberut, Indonesia

Abstract

Abundance and community structure of Mentawai primates in the Peleonan forest, north Siberut, Indonesia M a t t h i a s W a l t e r t , C h r i s t o p h e A b e g g , T h o m a s Z i e g l e r , S u sa t a and K e i t h H o d g e s Abstract The island of Siberut in the Mentawai Archipelago, west of Sumatra, Indonesia, supports four of the five primate species endemic to the Archipelago, all categorized as threatened on the IUCN Red List. As a baseline for future research on the ecology and conservation of Siberut's primates we used a line-transect approach to survey primates in the Peleonan forest, site of the Siberut Conservation Project in northern Siberut. In 104 km of surveys we made a total of 391 observations of primates and estimated density and population sizes for the Project's 10.7 km 2 main study site. Overall primate biomass density was estimated to be 697 kg km -2 and abundances, in individuals km -2 , were: pig-tailed snub-nosed langur Simias concolor, 53.1; Siberut macaque Macaca siberu, 16.2; Kloss's gibbon Hylobates klossii, 8.9; Mentawai langur Presbytis potenziani, 8.2.These results confirm those from earlier studies that in undisturbed and unhunted primary forests S. concolor is more successful than the sympatrically occurring P. potenziani. Results for all species suggest considerable population sizes on the island and underline its importance for the conservation of Mentawai primates.

Group Structure and Physical Characteristics of Simakobu Monkeys (Simias concolor) on the Mentawai Island of Siberut, Indonesia

“…The present study confirms these earlier observations on group size and, since our own study was carried out in a peat swamp forest region, it also provides further support that peat swamp forest represents an important habitat for S. concolor [see also : Quinten, 2008]. These findings, together with the high abundance of S. concolor in the adjacent (mixed) primary rainforest of North Siberut (53.1 individuals/km 2 ) shown by Waltert et al [2008], indicate a relatively high carrying capacity of both habitats, situated in the northern periphery of the distribution range of S. concolor . The comparatively low level of forest degradation in this region combined with the relatively low hunting pressure exerted on S. concolor by the locals living in this area most likely explain the abundance of these primates in the Peleonan forest and emphasise the conservation significance of this region for this critically endangered species.…”

“…Despite widespread habitat destruction throughout most of the Mentawai Islands, Northern Siberut still possesses areas of relatively undisturbed rainforest cover and recent census data for the Peleonan forest [Waltert et al, 2008] indicate that S. concolor occurs in densities of up to 53.1 individuals/km 2 , considerably higher than estimates reported for other locations. Although hunting pressure in North Siberut is thought to be relatively low, and local inhabitants have traditionally shown considerable respect for their natural habitat and its resources, primates are still killed as an occasional source of animal protein.…”

Line Transect and Triangulation Surveys Provide Reliable Estimates of the Density of Kloss’ Gibbons (Hylobates klossii) on Siberut Island, Indonesia

“…The transect system around the station consists of 13 systematically placed transects each 1–3 km in length (Waltert et al . 2008). …”

“…Protocols, season, survey times, surveyed transects, and data analysis followed those of the last survey in the study area in 2005 (Waltert et al . 2008). We surveyed each of the 13 transects around the field station between six and eight times (mean 7.23, SD = 0.6), resulting in a total survey effort of 155.5 km.…”

“…2010) but several primatologists have discussed the possibility that this method is less efficient for some species, among them the members of the gibbon family Hylobatidae (Nijman and Menken 2005; Whittaker 2005; and see discussion in Waltert et al . 2008). Gibbons are small bodied arboreal apes found across eastern and southeastern Asia, Northwest India, and Bangladesh.…”