Bee diversity along a disturbance gradient in tropical lowland forests of south-east Asia

1. Bees are believed to be dominant pollen vectors in tropical forests, yet studies specific to bees in south-east Asia are rare. Regeneration and restoration of the rapidly disappearing lowland forests of this region are reliant on bees, thus there is an urgent need for forest bee data at the community level. 2. Bee communities of eight forested sites in Johor (Malaysia) and Singapore were surveyed three times each from February to August 1999 at the below-canopy level. These sites ranged from relatively undisturbed primary lowland dipterocarp forests to late secondary forests and exotic forests, including an oil palm plantation. We attempted to elucidate the environmental factors that correlated with the distribution of bees. 3. Bee abundance, in particular that of Apidae, was significantly higher in larger primary forests than other types of forests. However, bee species richness was higher in disturbed forests. 4. The distribution of bees was apparently influenced by variables closely related to forest disturbance and resource abundance, such as the density of big trees (diameter at breast height 30-40 cm), temperature and flowering intensity of trees and shrubs. 5. More stingless bees (Trigona spp.) were found where trees were larger and ambient conditions more constant but flowering intensities lower. 6. The differences between the bee communities in forests of urban Singapore and primary forests in Johor may indicate that ecological processes in the forests of Singapore, in particular pollination, may be changing. However, pollination may not be totally intact in the primary forests surveyed, as their bee communities seemed to be depauperate. 7. The role of important pollinators, especially bees, for the long-term survival of tropical lowland forests is poorly understood. Our study indicates that we urgently need more thorough understanding of pollination and pollinators, as some bee species appear to be disappearing from disturbed tropical lowland forests.