Seasonal Variation of Butterfly Diversity in Subtropical Urban Forests of Nepal

Butterflies exhibit seasonal dynamics in diversity and population in response to bioclimatic factors. However, their seasonal diversity remains poorly understood in urban landscapes. Therefore, we examined how butterfly diversity varies across seasons in the urban forests of Pokhara City, located in Nepal's subtropical region. We selected three urban forests-Banpale, Bhadrakali, and Shanti Ban Batika-to sample butterflies. We employed the Pollard Walk Survey method to collect data across all four seasons and analyzed various diversity indices, community composition, and indicator species. We also applied generalized linear mixed models (GLMMs) to assess the effects of precipitation and temperature on species richness and abundance. In total, 197 butterfly species, comprising 3344 individuals from six families, were recorded. The diversity and community composition differed significantly across seasons, with richness, Shannon, and Simpson diversities peaking during the monsoon and abundance peaking in the pre-monsoon. Winter recorded the lowest species richness, diversity, and abundance. Species like Pieris canidia, Eurema hecabe, Ypthima baldus, and Junonia iphita contributed most to the differences across seasons. Anthene emolus was associated with the pre-monsoon season, Lethe kansa and Athyma ranga were confined to winter, and several other species served as seasonal indicators. The family Nymphalidae dominated the butterfly community, with different families exhibiting notable seasonal variation in richness and abundance. Additionally, GLMMs found that precipitation alone has a significant positive effect on species richness, while the combined effect of precipitation and temperature negatively impacts both richness and abundance. This study highlights the importance of seasonality in shaping butterfly diversity and community composition in urban forests, offering essential insights for their conservation in urban landscapes.