Land use effect on butterfly alpha and beta diversity in the Eastern Himalaya, India

Conservation of biodiversity in agroecosystems is a global challenge as conversion of forest to agroecosystems has been one of the major causes for biodiversity loss through habitat transformation. The agroecosystems, especially those traditionally managed or organic, are reported to retain high biodiversity including endemic, specialists and conservation concern species. Among others, butterflies are the most vulnerable taxa reacting sensitively and rapidly to climate and habitat changes, and represent as bio-indicators to predict the health of an ecosystem. However, the assessment of land use effect on butterfly diversity has not yet been undertaken in the Eastern Himalayas. Therefore, this study was designed along agroecosystem-forest gradient to understand: the patterns of butterfly alpha diversity taking into account the variation across seasons, elevation, forest specialization and larval host specificity; the patterns of butterfly beta diversity; and plausible environmental determinants of butterfly alpha and beta diversity. We assessed the patterns of taxonomic alpha and beta diversity of butterflies and their determinants in the Indigenous Farming Systems (IFS) {large cardamom-based agroforestry systems (LCAS), mandarin orange-based agroforestry systems (MOAS) and farm-based agroforestry systems (FAS)} along with adjacent natural forests (Forests) in the study area during December 2012–August 2017. We recorded 268 species of butterflies from six families which included two-third forest specialists, one-third monophagous and one-fifth conservation concern species. Along the agroecosystem-forest gradient, alpha diversity of butterflies declined for total, forest specialists, monophagous and protected species. However, pair-wise beta diversity increased and the multiple beta diversity was dominated by substitution components. Alpha diversity was determined by tree species richness, tree density, canopy cover, elevation, mean annual precipitation (MAP), season, whereas tree species richness, tree density, tree basal area, canopy cover, elevation, mean annual temperature, and MAP influenced beta diversity. We also identified 15 indicator species dominated by forest specialists suitable for long term ecological monitoring program in the Eastern Himalaya. The organic and traditionally managed agroecosystems of Sikkim play a complementary role to the protected areas (PAs) in fostering biodiversity conservation and ecosystem service provision, especially in the areas with high human pressure and low PA and forest coverage.