Diversity and distribution of Diptera in the canopy of primary and disturbed SE-Asian lowland rain forests

From 1991 to 2000 arboreal arthropod communities were collected in a SE-Asian primary lowland rain forest and in three types of secondary forests by insecticidal knockdown fogging. From all 115 fogging samples, a total of 33 239 specimens of Diptera was separated and sorted to 71 families. The aim of the study was to investigate how anthropogenic disturbance changes primary forest communities. The family composition of Diptera was very uniform within and between forest types, and always more than 85% of all Diptera belonged to ten families. The Chloropidae, Sciaridae and Ceratopogonidae followed by the Milichiidae and Phoridae were most abundant. In the disturbed forests, only the Lauxaniidae had increased significantly in numbers. Decolonisation dynamics were investigated by up to six consecutive daily refoggings of individual trees. During the course of the refoggings, the numbers of individuals of families of Diptera varied greatly and it was not possible to predict which family would be most abundant in a tree. This indicates that the decolonisation dynamics of trees are greatly influenced by stochastic processes. Almost no autecological data exist about most of the arboreal species. An assessment of species numbers in all fogging samples indicate that Diptera are one of the so called 'mega diverse' groups. Diptera are often neglected in ecological research although there is no doubt that they significantly influence many ecosystem processes. There is evidence that estimations of global species numbers would be significantly higher if Diptera, along with other highly diverse taxa, were adequately considered.