Disentangling the effects of host resources, local, and landscape variables on the occurrence pattern of the dusky large blue butterfly (Phengaris nausithous) in upland grasslands

Determining the effects of local and landscape drivers on endangered species and predicting potential suitable habitats for their persistence is crucial for effective conservation management. Here, we applied a multi-scale approach to disentangle the effects of host resources, local, and landscape variables on the occurrence pattern of Phengaris (= Maculinea) nausithous in semi-natural upland grasslands. Our approach comprised the assessment of host parameters (plant cover, density, height, flower heads density, ant nest density, ant colony size), local grassland management (pasture, meadow), site conditions (area, shape, terrain attributes), and landscape variables (landscape composition, connectivity). We used ensemble of small models based on bivariate generalized linear models for explaining and predicting the butterfly occurrence pattern. Bivariate models revealed that host ant nest density, plant cover and height, local grassland management type (pasture), slope and eastness, landscape forest cover and grassland connectivity had a positive effect on the occurrence of P. nausithous (average explained deviance 20.5%). Host ant density, host plant cover, and local grassland management were the most influential factors on the ensemble predictions. The presence of P. nausithous in upland grasslands is not only determined by host resources, but also by local and landscape factors. Such factors proved to be relevant for identifying and predicting suitable grassland sites for this endangered species. Consequently, we recommend that conservation actions should include a landscape perspective to promote connectivity by facilitating coherent grazing networks enabling dispersal between semi-natural upland grasslands and thus species persistence.