“Pollard-walk” Butterfly Survey does not Warrant the Equity of Sampling-completeness among Butterfly Families: A Case Study with Tropical Butterfly Fauna in Bhutan

Abstract

Complete or even sub-complete inventories of biodiversity often remain well out of reach, especially when dealing with speciose taxonomic groups, such as insects in general and butterfly fauna in particular. Moreover, it is even uncertain that similar completeness levels may be reached among taxonomic subsets within a same surveyed taxonomic group. For example, one can wonder whether sampling butterfly fauna according to the commonly implemented “Pollard walk” consistently ensure a similar recording efficiency (i.e. similar sampling completeness) according to the different butterfly families. To address this issue and quantify the possible unevenness of sampling completeness between five main butterfly families, we consider a “Pollard walk” butterfly survey of tropical butterfly fauna, carried out along Sankosh River (Bhutan) by Arun P. Singh. Reasonably accurate estimates of the true total species richness and the corresponding sampling completeness were derived, for each butterfly family, by implementing the recently developed procedure of “least-biased” extrapolation of the species accumulation curve. Whereby, a reliable evaluation of the level of sampling completeness is obtained for each butterfly family. For the inventory under consideration, a significant scatter of sampling completeness levels between the five families is highlighted: sampling completeness levels range from 65% for Lycaenidae to quasi exhaustivity for Papilionidae, with intermediate levels for the other three families. These findings revealed that “Pollard walk” survey may lead to appreciable differences of sampling completeness level among the different butterfly families. Besides, this study provides a reliable estimate of the total species richness of butterfly fauna in the surveyed ecosystem, amounting to no less than 280 species concentrated in a rather reduced area along Sankosh River.