Impact of urbanisation on the diversity and abundance of butterflies along an urban gradient in Guwahati, Assam, India

Urbanisation is one of the leading drivers of biodiversity loss world-wide, yet its ecological effects in tropical and subtropical regions remain poorly understood. In rapidly developing South and Southeast Asian cities, including Guwahati in northeast India, the transformation of forested hills into urban landscapes poses major challenges for native insect communities. Understanding how such habitat change influences butterfly diversity is critical for biodiversity conservation within the Indo-Burma biodiversity hotspot. We aimed to quantify butterfly diversity and abundance along an urban gradient in Guwahati and to evaluate how habitat transformation affects species richness, community composition, and ecological turnover. Standardised transect surveys were conducted across 12 sites representing three habitat categories, and community patterns were analysed using diversity indices, β-diversity partitioning, and Generalised Linear Mixed Models (GLMMs). We recorded 3,594 individuals representing 174 species across six families. Butterfly richness and diversity declined markedly from forest to urban habitats, while community composition differed significantly across the gradient. β-diversity was high and mainly driven by species turnover, indicating replacement of forest specialists by disturbance-tolerant generalists. GLMM analyses confirmed that habitat type strongly influenced species richness but not overall abundance, reflecting the dominance of a few adaptable taxa in urban settings. These results provide new insights from northeast India on how urbanisation filters butterfly communities through habitat loss and turnover. Preserving and restoring remnant forest patches within Guwahati’s urban matrix will be crucial for sustaining native insect diversity.