Effects of temporal and spatial continuity of grasslands on butterfly communities

Abstract Semi-natural grasslands have high biodiversity, but they are declining worldwide, and desperately need to be prioritized for conservation. Recently, numerous papers have concluded that vegetation history may influence biodiversity. We targeted three vegetation types in ski-run grasslands in central Japan: "old grasslands" that have been in existence for 300 to several thousand years, "new grasslands" that have been deforested for 43 to 72 years, and forests adjacent to those ski-runs. We established transects at six to seven sites for each vegetation type and surveyed butterfly communities visually. Plant communities were also surveyed along the same transects. Species composition, numbers of species, and total abundance of butterflies did not vary with grassland age; however, the area of old grasslands within 100 m of transects affected species composition. Minois dryas (Nymphalidae) and Eurema mandarina (Pieridae) were identified as indicator species of large, old grasslands (>8000 m2 within 100 m), whereas no indicator species were detected at other sites. Abundances of Minois dryas, Brenthis daphne (Nymphalidae), and Curetis acuta (Lycaenidae) were greater where old grassland areas occurred within 100 m of observed sites. Sanguisorba officinalis (Rosaceae), the host plant of B. daphne, and Lespedeza bicolor, the main host plant of E. mandarina and C. acuta, was identified as an indicator of old grassland, explaining the dependence of these three butterfly species on old grasslands. Previous studies have also shown that M. sinensis, the main host plant of M. dryas, is an indicator for the entire grassland, suggesting that the butterfly's distribution was restricted to a narrower area than that of host plants. Our results suggest that large, old grasslands should have high conservation priority to maintain grassland butterfly diversity.