Orangutans are the only great ape recorded in tropical Asia. Two species of orangutans are found, i.e. Pongo abelii in Sumatra and P. pygmeus in Borneo.
Sumatran orangutans (SOUs) are strictly distributed in the Northern Sumatra and their populations are drastically reduced and are gradually decrease. The main factors of decline are the habitat loss due to deforestation and forest degradation (1) and also a long mean inter-birth interval (2).
van Schaik et al. (3) stated that the tree availability, as food sources and nesting sites for orangutan population in the tropical forest ecosystem, has become the most influential factor on density of orangutans.
Vegetation analyses were carried out to identify tree species diversity and tree species as feeding source of Sumatran orangutan (SOU) in Batangtoru forests. The 378 tree species are recorded within 20 plots or the total area is 0.8 ha. Only 173 tree species (46%) are as feeding sources of SOU.
1 Rijksen, H.D. & Meijaard, E (1999) Our Vanishing Relative: Status of Wild Orangutan at the Twentieth Century. Dordrecth, Netherlands: Kluwer Academic Publisher.
2 Galdikas, B.M.F., Wood J.W. (1990) Birth spacing patterns in humans and apes. American Journal of Physical Anthropology 83:185—191
3 van Schaik, C.P., Priatna, D., Priatna, A. (1995). Population estimates and habitat preferences of orang-utans based on line transects of nests. In The Neglected Ape (eds R.D. Nadler, B.M.F. Galdikas, L.K. Sheeran & N. Rosen), pp. 129–147. New York, USA: Plenum Press.
Part of this research will be presented by Onrizal and Mashhor Mansor at the 2014 AAAS Annual Meeting on 13-17 February 2014 in Chicago, IL, USA