A Numerical Analysis of Tropical Rain Forest, Using Floristic and Structural Data, and Its Application to an Analysis of Gibbon Ranging Behaviour

Abstract

As part of a study of the manner in which Kloss gibbons use the forests available to them, data were collected in 2 study areas of lowland evergreen rain forest on Siberut Island, Indonesia, from 2459 trees of at least 15-cm dbh along transects of quadrats the total area of which was 11.3 ha. The identity of each tree, its height and climber load, the abundance of Myrmecodia epiphytes, and the position of its crown within the neighboring canopy were recorded. Analysis of these data using classification and ordination techniques yielded 9 forest types which could be interpreted ecologically. One was on dry level ground, 1 on wet level ground, 1 on peat swamp, 2 on major ridges and 4 on minor ridges. These types were generally recognizable by indicator species. Seven of the forest types, 22 blocks, were in the 31-ha home range of the main study group of gibbons. The number of times that gibbons were seen feeding in a forest type was very highly correlated with the density of trees that were potential fruit sources for gibbons. Female gibbons sang from those forest types with the trees that were tallest and above the break of slope. The gibbon group slept in those forest types in which the trees had a low frequency of the myrmechophilous epiphyte M tuberosa, presumably to avoid being bitten by ants. Few meaningful correlations were found between forest type and speciic activities, but forest types such as peat swamp were under-used consistently, while others such as those on minor ridges were used disproportionately often for certain activities. This information allowed the conventional 2-dimensional view of a home range to be extended to a 4-dimensional view by including differential canopy use and changes in behavior through the day.