Impact of Habitat Changes on Butterfly Diversity in the Forest–Grassland Ecotone in the Source of the Bailong River, Western China

Habitat type and elevational gradient are key drivers shaping biodiversity variation in alpine montane grasslands. To explore the effects of habitat type on butterfly communities and their variation along the elevational gradient in the forest–grassland transition zone at the source of the Bailong River, we conducted transect surveys over three consecutive years (2022–2024). The main results are as follows: (1) The butterfly community showed typical characteristics of alpine grassland assemblages, dominated by Nymphalidae (60.0%), while Lycaenidae accounted for 13.0%, followed by Pieridae (23.7%). Papilionidae and Hesperiidae accounted for very low proportions, at 0.7% and 0.5%, respectively. (2) The ecotone generated pronounced habitat edge effects; the forest-edge shrub habitat harbored the highest species richness. (3) Species-composition similarity of butterfly assemblages among habitats was low. (4) The vertical distribution of butterfly species exhibited a distinct double-valley pattern. (5) Parnassiinae species inhabiting high-elevation alpine meadows face major threats from climate change. Conservation implications: Butterfly conservation within this alpine watershed requires coordinated ecological management that balances socioeconomic development and biodiversity protection. Endemic high-elevation butterfly species should be treated as priority conservation targets for future biodiversity management in the Bailong River source area.