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

Abstract

Beta (β)-diversity varies along environmental gradients, and understandingwhat 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 fixedwidth 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.

Temperature seasonality drives taxonomic and functional homogenization of tropical butterflies

“…High species turnover in mountainous terrain is not uncommon (e.g. Dewan et al., 2022) and can be attributed to environmental heterogeneity (Wilson & Fox, 2021). Functional richness was projected to be the greatest in the humid, north‐west region of the island, where taxonomic richness was also projected to be high.…”

“…Another possibility is that thermal stability reduces selection for traits that cope with unstable temperature regimes and these traits then vary simply by genetic drift. The impact of temperature seasonality on species turnover is much less understood, and on functional turnover even less so (Dewan et al., 2022). Seasonality may impact species and functional turnover through its impact on resource availability (Gaston & Chown, 1999).…”

Geography of Indian Butterflies: Patterns Revealed by Checklists of Federal States

“…Recently, there has been an explosion of diversity patterns studies conducted at smaller scales, with a notable bias towards biodiversity hotspots (e.g., Western Ghats [ 34 ], Eastern Himalaya [ 35 , 36 ]). Species-poorer peninsular India remains neglected [ 37 , 38 ]. Reflecting the explosive increase in knowledge, new comprehensive checklists on Indian butterflies were produced by Varshney and Smetacek [ 39 ] and Gasse [ 40 ].…”

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

“…Hence, understanding the distributional pattern and range size of such a vulnerable group of organisms serves as baseline information for predicting the impact of climate change and anthropogenic disturbance. Moreover, such studies are important on mountain landscapes such as the Himalaya where climate change and anthropogenic pressure have a profound impact (Singh et al, 2011), but where vulnerability assessment of lower taxa such as insects is scarce due to a lack of baseline information (Acharya & Vijayan, 2015;Dewan et al, 2021Dewan et al, , 2022. Due to the extreme range of elevational span and varying climatic gradient, the Himalaya offers a unique opportunity to test biogeographic hypotheses such as Rapoport's rule.…”

“…For instance, butterflies affiliated with the Palearctic region demonstrate a broad environmental tolerance, resulting in larger ranges compared to Oriental butterflies, which typically are confined to tropical areas (Holloway, 1974). In fact, exploration of species richness, density, and community composition patterns of butterflies along the elevation gradient in the Eastern Himalaya reveals that not every butterfly group demonstrates elevation patterns that align with the overall community trend (Dewan et al, 2021(Dewan et al, , 2022. Thus, grouping butterflies according to their traits and taxonomic affiliation may allow for the unveiling of differences in elevational range patterns and responses to abiotic and biotic factors.…”