Vertical Stratification of Ambrosia Beetle Assemblage in a Lowland Rain Forest at Pasoh, Peninsular Malaysia

Abstract

We report the vertical profile of the species assemblage of ambrosia beetles in a primary forest stand at Pasoh Forest Reserve (Pasoh FR). Ambrosia beetles (xylomycetophagous species of the families Scolytidae and Platypodidae) live in wood, feeding on symbiotic fungi growing on the walls of their galleries. In order to clarify the vertical structure of the assemblage in a tropical rain forest, we used collision traps with ethanol as an attractant set on canopy towers in the forest. In total, 42 species of ambrosia beetles were captured in the ethanol traps placed serially from 1 m to 32 m above the ground. They showed a bi-modal pattern of species distribution in the median height of collection, suggesting that the species are largely divided into canopy species and understorey species. It seems likely that about three quarters of the species are canopy species, probably flying in the main canopy and somewhat shaded subcanopy layers, and most others are understorey species, foraging just above the forest floor. Host taxon selection was not differentiated between the canopy species and the understorey species. However, the canopy species were rather specific to branches of a certain size for each species while the understorey species were mostly generalists in host size selection. Ambrosia beetles are expected to promote early decomposition of wood materials through boring galleries into the wood and infecting them with wooddecaying fungi. Our results suggest that they are rich in species in the forest canopy, where they play an important role in early decomposition and rapid breakdown of standing branches, while some others are confined to the understorey or forest floor, attacking the fallen branches and bigger limbs of trees as well as seedlings.