Abstract
Forest-grassland mosaics are phytophysiognomies of grassland and forest ecosystems that create strong environmental contrasts, influencing species distribution in biomes like the Pampa of Southern Brazil. Our study analyses the structure of fruit-feeding butterfly (Nymphalidae) assemblages across natural mosaics of native grasslands and forest fragments in the Pampa biome in relation to butterfly abundance, species richness and composition in forest and grassland habitats across six localities. Our results show that forest habitats generally support higher richness and abundance, and harbor distinct butterfly communities compared to native grasslands. Species composition clearly segregated the two habitats, reflecting differences in environmental conditions, structural heterogeneity, and resource availability. Forests supported more taxonomically diverse assemblages due to vertical stratification and microclimatic heterogeneity, although local disturbances like cattle grazing and flooding could impact diversity. The dominance of the Satyrini tribe, particularly in disturbed forest fragments, suggests that anthropogenic impacts simplify forest structure, favoring disturbance-tolerant species. Native grasslands were also dominated by disturbance-tolerant Satyrini adapted to open conditions. The study demonstrates that habitat type strongly structures fruit-feeding butterfly assemblages and suggests that this group has the potential to serve as effective bioindicators for monitoring the impacts of land use in this heterogeneous landscape. Implications for insect conservation Findings emphasize the urgent need to integrate both forest and grassland habitats into conservation policies, as each supports unique and distinct butterfly assemblages, collectively reflecting the ecological heterogeneity of the Pampa biome.