Beetle assemblages in rainforest gaps along a subtropical to tropical latitudinal gradient

Abstract

Successional processes in forest gaps created by tree falls are often considered a principal mechanism maintaining species diversity within forests. Although insects are important as mediators of forest recovery processes, there have been few observations of how they differ between forest gaps and non-gaps across latitudes. Here we tested the impacts of gap habitat on beetle assemblage composition at three locations spanning sub-tropical and tropical biomes (28°S, 16°S, 5°N: Lamington and Daintree in Australia, and Danum in Borneo). Beetles were collected by flight interception traps and sorted to family and feeding guilds. Despite clear differences in environmental conditions between gaps and non-gaps at all three location, we found weak and inconsistent differences in beetle family and feeding guild composition across a latitudinal gradient. PERMANOVA results showed no significant differences in beetle family and feeding guild composition between gaps and non-gaps. For beetle families, however, the interaction effect (between gap vs. non-gap treatment and location) was significant. Post-hoc analysis and NMDS ordinations showed significant and clear separation of family assemblages between gaps and non-gaps within the Danum samples but not within samples from either the Lamington or Daintree sites. Using IndVal, when all three locations were combined, Chrysomelidae and Tenebrionidae were found to be indicators for gaps and Scarabaeinae and Leiodidae for non-gaps. Analysed separately, gap indicators were only Chrysomelidae at Daintree, whereas non-gap indicators were Scarabaeinae at Lamington, Scarabaeinae, all other Scarabaeidae, Anthicidae, Scydmaeninae, and Hybosoridae at Danum. We suggest the scale of changes in insect composition and richness with the creation of a natural light gap in forests contrast with those resulting from anthropogenic disturbance such as logging and clearing of forests and the greater adaptability of forests to small-scale changes rather than large-scale changes.