Moth, beetle, and bug assemblages are shaped differently across a tropical rainforest vertical gradient

Abstract

Tropical forests harbour a large proportion of Earth’s insect biodiversity. Tropical forest structure produces layers of habitat from the cooler, wetter understorey to the hotter, drier canopy, which provide stratified resources for inhabitants. This gradient of biotic and abiotic factors results in vertically stratified insect communities, often with different assemblages in the understorey and canopy. Vertical distributions of insect taxa are shaped by their niche requirements, with narrower vertical ranges for species with more specialised life history strategies and abiotic requirements. Many studies of vertical stratification focus on single taxonomic orders, often overlooking less well-worked orders, such as Hemiptera, and comparisons of the responses of different taxa sampled at the same time under the same conditions are rare. Here we examine light-trapped samples of adult Lepidoptera (moths), Hemiptera: Auchenorrhyncha (leafhoppers and relatives) and Coleoptera (beetles) collected at 0 m, 10 m, 20 m and 30 m from the ground within a primary tropical forest in Daintree, Queensland, Australia. We found different assemblages of insects in the canopy (20–30 m above ground) and in the understorey (0–10 m) for moths and beetles, but not for Auchenorrhynchs. Species diversity of moths was higher in the canopy than in the understorey, while beetles showed the opposite pattern. In contrast, Auchenorrhyncha did not vary in species diversity between the canopy and the understorey. This may be because the resources used by moths are mostly higher in the canopy and vice versa for beetles. Auchenorrhycha are sap-sucking insects so, provided their host plants can be found throughout the vertical gradient, they might not face the resource availability pressure that drives stratification in moths and beetles. We suggest that future studies of vertical stratification in multiple taxa need to test for such drivers of diversity.

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