Rapoport's rule explains the range size distribution of butterflies along the Eastern Himalayan elevation gradient

Understanding elevational range size distribution of organisms can provide valuable insights on biogeographic pattern of species and their conservation. Rapoport's rule posits that the elevational range size of species increases with increasing elevation. However, the validity of this rule is often questioned due to variations in methodologies across studies and inconsistencies among different groups of organisms. In this study, we examined the elevational range size distribution of butterflies in the Eastern Himalaya, and assessed the applicability of Rapoport's rule using different approaches, which perhaps is the first of its kind in the Himalaya. We sampled butterflies along the elevational gradient of 16 elevational bands (300–3300 m) using point count method along the transect. The sampled butterflies were grouped into various sub-groups based on family, biogeographic affinity, and larval feeding pattern. We found that the majority of the butterfly species (total as well as sub-groups) had small range sizes, and their elevational range distribution showed support for the Rapoport's rule. Increase in variation in temperature as measured by temperature seasonality and mean annual temperature range were the most important predictors of range size distribution pattern of the overall butterfly community. However, the relationship between range size and climatic variability differed among various sub-groups implying that the perceived pattern may vary even within the species of the same taxon.

Abstract in Nepali is available with online material.