Vertical distribution of beetles in a tropical rainforest in Sulawesi: the role of the canopy in contributing to biodiversity

1. The extent to which forest canopies contribute to global biodiversity, and the degree of strata-orientation shown by forest insects, remain open questions. The vertical distribution of nocturnal flying beetles in tropical rainforest in Sulawesi was examined, and the extent to which stratum preferences occurred, in order to establish the relative importance of the forest canopy in shaping rainforest communities. 2. Samples were collected using actinic light traps set from the high canopy (30 m) to ground level. 11 ,692 specimens collected over one lunar month were sorted to 701 species within 65 families. The greatest abundance, species richness and diversity were recorded in the canopy, with a decrease in all measures towards the ground. The sample was analysed at family and species level, with correlation analysis showing the greater number of canopy specialist families and species found in the canopy compared to the ground. 56% of more abundant species showed no stratum preference, and of those species that did, 39% were specific to the canopy and 5% to the ground layer. 3. The structure of samples from each level of the forest showed remarkable uniformity in terms of numbers of singletons and doubletons as a proportion of the total sample. This suggested conformity of species assemblage structure, and underlying processes shaping these assemblages, at different heights. 4. The study was examined in relation to other literature on the vertical distribution of insects in tropical forests. As with other studies, many of the more common species were distributed throughout the forest, although in the present study a significant portion showed stratum preferences, and the majority of these showed strata-orientation to the forest canopy. This work reiterates the need to sample through multiple dimensions in order to accurately measure species richness and diversity in tropical forests and estimate global biodiversity, and the importance of maintaining the dimensional integrity of the forest when conserving rainforest ecosystems.