Applicability of butterfly transect counts to estimate species richness in different parts of the palaearctic region

Abstract

Transect counts are one of the most popular approaches to assess and monitor butterfly diversity, especially with the background of biodiversity loss. This method was developed in Europe, but its transferability is seldom tested across the world. To assess transferability, we compared butterfly richness estimates based on transect counts in Spain, Germany and central China, a region with a considerably different biogeographic history and more diverse butterfly fauna compared to Europe. We found that the efficiency of transect counts was much lower in China than in the other two regions. Apart from the fact that traditional transect counts may undersample canopy species which are predominant in central China, higher efficiency in Europe may be primarily attributed to different patterns of butterfly richness likely caused by different biogeographic and anthropogenic land-use history. Our results highlight that great caution is needed when transect count methods are transferred to other regions of the world, especially to particularly species rich areas with a high number of rare species. Low detectability of certain species can substantially mask species richness estimates, and we suggest to carefully adapt sampling effort and perhaps combine transect counts with other methods to ensure more realistic assessment of species richness in such regions.