Comparison of rainforest butterfly assemblages across three biogeographical regions using standardized protocols

Abstract

Insects, like most odter organisms, are more diverse in tropical than in temperate regions, but standardized comparisons of diversity among tropical regions are rare. Disentangling the effects of ecological, evolutionary, and biogeographic factore on community diversity requires standardized protocols and long-term studies. We compared the abundance and diversity of butterflies using standardised 'Pollard walk' transect counts in die understory of closed-canopy lowland rainforests in Panama (Barro Colorado Island, BCI), Thailand (Khao Chong, KHC) and Papua New Guinea (Warning, WAN). We observed 1792, 1797 and 3331 butterflies representing 128,131 and 134 species during 230,231 and 120 transects at BCI, KHC and WAN, respectively. When corrected for length and duration of transects, butterfly abundance and species richness were highest at WAN and KHC, respecuvely. Although high butterfly abundance at WAN did not appear to result from methodological artefacts, the biological meaning of this observation remains obscure. The WAN site appeared as florisdcally diverse as KHC, but supported lower butterfly diversity. This emphasizes that factors odier than plant diversity, such as biogeographic history, may be cnicial for explaining butterf ly diversity. The KHC butterfly fauna may be unusually species rich because the site is at a biogeographic crossroads between the Indochinese and Sundaland regions. In contrast, WAN is firmly widiin the Australian biogeographic region and relatively low species numbers may result from island biogeograpbic processes. The common species at each of the three sites shared several traits: fruit and nectar feedeis were equally represented, more than half of common species fed on eidter epiphytes or lianas as larvae, and their range in wing sizes was similar. These observations suggest that Pollard walks in different tropical rainforests target similar assemblages of common species, and, hence, represent a useful tool for long-term monitoring of rainforest butterfly assemblages.