Understorey versus canopy: patterns of vertical stratification and diversity among Lepidoptera in a Bornean rain forest

We studied the vertical distribution of Lepidoptera from a canopy walkway w ithin a dipterocarp rain forest at Kinabalu Park (Borneo) using three diffe rent methods: (1) Bait traps to survey fruit-feeding nymphalid butterflies, (2) standardized counts for predominantly flower-visiting butterflies and their potential predators, aerial-hawking birds, and (3) attraction by blac klight for hawk- and tiger moths. There was a distinct decrease in the abun dance of fruit-feeding nymphalids towards the canopy, probably due to a red uced and less predictable availability of rotting fruits in higher strata. These constraints might also be responsible for a higher abundance variatio n in the canopy, and a significant shift in size from larger species in the understorey to smaller ones in the canopy. Changes of microclimate and the conspicuous increase of insectivorous aerial-hawking birds from ground to canopy layer may be responsible for the prominent change in species composi tion of fruit-feeding nymphalids between 20 and 30 m. Nectar-feeding Lepido ptera showed a reversed abundance pattern. One main factor contributing to the much higher abundance of flower-visiting butterflies and moth taxa in t he canopy, such as Sphingidae and some Arctiinae, might be the increase of nectar resources available in upper vegetation layers. A distinctly higher diversity in hawkmoths was also found in the canopy. A higher abundance of insectivorous aerial-hawking birds in the canopy might contribute to the sh ift in body design of fruit-feeding nymphalids from more slender bodies at lower vegetation layers to stouter ones (i.e. species which are stronger on the wing) in the canopy. Larval resources could play an additional role in specialisation on but a small part of the vertical gradient. This may expl ain stratification pattern of the nymphalid subfamilies Morphinae and Satyr inae. Monocotyledoneous larval food plants of both taxa, whose flight activ ity is largely restricted to the understorey, occur mostly in lower vegetat ion layers. Our observations on a wide taxonomic and ecological range of bu tterflies and moths indicate that tropical forest canopies hold a distinct and unique Lepidoptera fauna, whose species richness and abundance patterns differ from lower strata. However, the notion of tropical forest canopies as peaks of terrestrial diversity does not hold uniformly for all taxa or g uilds.