POPULATION MAPPING OF GIBBONS IN KALIMANTAN, INDONESIA: CORRELATES OF GIBBON DENSITY AND VEGETATION ACROSS THE SPECIES RANGE

摘要

The first comprehensive survey of gibbons across peatlands in Indonesian Borneo was carried out over three years to 1) determine population density in the survey areas and threats to these areas; and 2) determine if densities of gibbon species correlate with vegetation characteristics and, if so, whether the same characteristics are correlated with density across all forest types. To achieve this, a total of five forest blocks were surveyed, involving 31 independent survey locations and repeat surveys in three forest blocks. Our data show that gibbons are ubiquitous where there is forest but forest quality affects population density, especially in peat-swamp forests. Forest block size affects longevity of populations and populations are susceptible to the 'compression effect' i.e. population overcrowding at unsustainable densities, especially in areas where there are contiguous habitat sub-types with variable characteristics. We show the effects of forest disturbance (logging, fragmentation, drainage and fire) on gibbon distribution and density. We discuss the importance of remaining peat-swamp forests as refuges for viable populations of gibbons and highlight issues for long-term conservation in this habitat. The use of minimum cross-sectional area, density of figs and fallback foods, habitat variables and presence of top foods are considered as determinants of population density to identify population thresholds below which gibbons cannot persist.