Habitat quality determines patch occupancy of two specialist Lepidoptera species in well-connected grasslands

Over the past 150 years, semi-natural grasslands have suffered from either large-scale intensification of land use or abandonment. Lepidoptera are excellent model organisms to study the effects of land-use changes. In this study, we analysed the effects of landscape quality and habitat quality on the patch occupancy of twospecialist Lepidoptera species, the butterfly Erebia medusa and the burnet moth Adscita statices, in small but well-connected semi-natural grasslands (N=71) in central Germany. Our study revealed that habitat quality was the main driver of patch occupancy of the two species. The generalized linear model analysis revealed that the occurrence of both species was determined by the litter volume. Additionally, for A. statices the cover of the host plants (Rumex acetosella and R. acetosa) was a further predictor. In contrast, landscape quality had only a minor role on patch occupancy. For both species, the observed population structure resembled a classical metapopulation of the Levins type consisting of many small and highly connected patches. In the short and medium term, abandonment was beneficial for both species, as it maintained the litter layer. In the long run it would lead to vegetation dominated by competitive, high-growing grasses (e.g., Arrhenatherum elatius) and a decreasing cover of the less competitive host plants, especially Festuca ovina agg. and R. acetosella. Hence, we would recommend rotational grazing or mowing, if sufficiently large parts of the habitats were not under management every year.