Turnover in butterfly communities and traits along an elevational gradient in the eastern Himalaya, India

Abstract

Beta (β)-diversity varies along environmental gradients, and understanding what drives such variation might provide insights into the factors that shape community structure from place to place. Here, we delineate the spatial pattern of β-diversity, analyze its underlying mechanisms, and examine variation in functional traits of butterflies along an extensive elevational gradient (300–3000 m) in the eastern Himalaya, the largest mountain system in the world. We sampled butterflies at 16 sites along this gradient using a fixed-width point count method and estimated habitat variables at each site. We obtained trait data from our field collections and secondary sources as necessary. We partitioned β-diversity into its turnover, nestedness, balanced variation, and abundance gradient components. We used generalized dissimilarity modeling to determine the underlying mechanisms affecting the pattern of β-diversity along the gradient. The pattern of β-diversity in butterflies at adjacent sites exhibited a mid elevation peak. Dissimilarity between sites increased with the increase in distance between the sites. Turnover or the balanced variation made major contributions to the overall β-diversity. Among the set of factors, actual evapotranspiration was positively correlated with β-diversity. The trait-based analysis revealed biogeographic affinity as the best predictor of community composition along the elevational gradient. The high β-diversity arises from turnover rather than nestedness component. We conclude that the pattern of β-diversity of butterflies in the Himalaya is largely due to environmental filtering rather than geographic extent.