Written by Dr. Susan Cheyne (BNF’s Co-director)
The recent report of 100k orangutans having died in Borneo over a 16 year period have brought attention back to the high rates of deforestation prevailing in Borneo and its devastating impact on its unique primate fauna. Analysis by UNEP indicates that Borneo has lost a significant chunk of its forests till date. According to WWF, Borneo is poised to lose more than 21.5 million hectares of forest cover from 2007 to 2020.
Out of all the regions/parts of Borneo, Kalimantan has faced among the highest rates of forest loss. Between 2009 to 2011, 296000 hectares of forest were lost in Central Kalimantan and 38% of this loss was owing to the creation of new oil palm plantations. Creation of new oil palm plantations is also linked with forest fires and road construction. These factors, along with habitat can potentially have a devastating impact on the primate species of the region.
In our research, we investigated how forest-structure variables and landscape scale anthropogenic disturbance factors influenced the life-history behaviours (sleeping, ranging and feeding) of two endemic and sympatric primate species, Presbytis rubicunda (red langur) and Hylobates albibarbis(Bornean agile gibbon), in Sabangau tropical peat-swamp forest, Central Kalimantan.
We aimed to identify key factors that influence habitat suitability for both species, and determine the influence of similar factors when selecting habitat for various activities such as sleeping, feeding and ranging. GPS locational data for each behaviour were analysed in conjunction with forest-structure parameters present (derived from LiDAR, ALOS-PALSAR), landscape-scale habitat-related factors, and proximity to landscape-scale disturbance factors including burned areas. A Maximum Entropy (MaxEnt) algorithm was employed for estimating habitat suitability for the different activities of each species based on the aforementioned variables.
By using a combination of forest sub-class, structure and disturbance variables within the MaxEnt framework, distribution maps of suitable langur and gibbon sleeping, ranging and feeding habitats were produced. Langurs and Gibbons had limited overlaps in terms of feeding, ranging and sleeping habitats. In all cases, landscape-scale variables including those related to landscape-scale anthropogenic disturbance had the highest percentage contribution for explaining habitat suitability in comparison to forest-structure variables such as canopy heights (derived using LiDAR data). Additionally, variables influencing habitat selection varied between species; while langur feeding, ranging and sleeping were all influenced by distance from burned forests, gibbon sleeping habitat selection was influenced by distance from the forest edge, and ranging and feeding habitat selection was most affected by distance from burned areas. The insights gained from this study may help inform conservation management of these species and guide forest management strategies accordingly to ensure habitat structure is maintained to facilitate activities by sympatric primate species.
