Date Published: July 31, 2019
Publisher: Public Library of Science
Author(s): Susan M. Cheyne, Bernat Ripoll Capilla, Abdulaziz K., Eka Cahyaningrum, David Ehlers Smith, RunGuo Zang.
Gibbons are highly territorial and have two key areas within these territories. The core area in which we find all sleeping trees and the trees from which the gibbons duet and the wider home range (HR) which has varying levels of overlap with neighbouring gibbon groups. The core area is strenously defended, with the wider HR being more of a shared area for neighbouring groups. We present ranging and movement data on four wild gibbon groups from January 2010 to July 2018. Global Positioning System (GPS) data were collected every 5 mins on habitauted groups in Sebangau, Central Kalimantan, Indonesia resulting in 35,521 waypoints. Gibbon home- and corerange sizes were calculated using 95%, and 50%, volume contours of kernel density estimates. Home-ranges ranged from 58.74–147.75 ha with a mean of 95.7 ± SD 37.75 ha, the highest of comparable Hylobates species. Core-range size ranged from 20.7–51.31 ha with a mean size of 31.7 ± SD 13.76 ha. Gibbons had consistant site fidelity for their home- and core ranges; percentage overlap ranged from 4.3 23.97% with a mean 16.5 ± SD 8.65% overlap in home-range area. Core ranges did not overlap with the exception of two groups, in which a 0.64 ha (2.69%) overlap occurred. Unsurprisingly forest loss from fire does affect the location of the HR of the impacted group, but does not appear to affect adjacent groups, though more data are needed on this. Understanding the complex use of space of these territorial animals is important in assessing both carrying capacity for wild populations and understading how reintroduced gibbon pairs will establish their core and HR.
Home range is defined as the area in which an animal normally travels during routine activities, such as food gathering, mating and caring for young . Home range estimation is important for the understanding of the species’ spatial and behavioural ecology [2–4]. Information about ranging patterns and its’ determinants are important for several reasons: this constitutes basic data for the study of social organization of a species, gives an indicator of the spatial needs for individuals and populations, and provides essential tools for conservation management, especially for species found in small, isolated or endangered habitats [2,5,6].
The study site is the National Laboratory of Peat Swamp Forest (NLPSF) managed by CIMTROP (Centre for the International Cooperation in management of Tropical Peatland). NLPSF is located at the NE part of the Sebangau Forest, Central Kalimantan, Indonesia (Fig 1). Sebangau catchment covers an area of 5600 km2 of peat-swamp forest [54,55]. The research area is 4 km2 of grid transects system, containing seven habituated gibbon groups. The Sebangau catchment is characterised by peat-swamp forest and low elevation, presenting three different forest types: mixed swamp forest, low pole forest and tall interior forest . Our study was carried in Mixed Swamp Forest (MSF) which occupies 40% of the total area of Sebangau forest . The MSF extends ~4km from the margin of the forest into the interior. It is beyond the locaiton of the river flooding zone. The forest is tall and stratified with an upper canopy at ~35m, a closed layer between 15-25m and an understorey of smaller trees at 7-12m. Trees grown on hummocks interspersed with hollows which fill with water during the wet season. Many of the species have stilt or butress root systems and pneumatophores are common. Typical trees of the upper and mid-canopy are Aglaia rubinigosa, Calophyllum hosei, C. lowii, C. sclerophylum, Combretocarpus rotundatus, Cratoxylum galucum, Dactylocladus stenostachys, Dipterocarpus corieus, Dyera costulata, Ganua mottleyana, Gonstylua bancanus, Mezettia leptopoda , Neoscortechinia kingii, Palaquium cochlearifolium, P. leiocarpum, Shorea blangeran, S. teysmanniana and Xylopia fusca [54,59].
The HR of the gibbons from Sebangau are the largest of all comparable Hylobates sp. studies (Table 4). A possible explanation is the peat-swamp habitat and associated variable food availability [18,56,65–68] and/or the population density of the area being lower than carrying capacity due to anthropogenic disturbances e.g. logging and fire [43,69–71].