Potential distribution models and the effect of climatic change on the distribution of Phengaris nausithous considering its food plant and host ants

Climate change has an effect upon the distribution of butterflies, affecting species that are already sensitive due to their specific ecological requirements. This is the case of Phengaris nausithous, an endangered species in the Iberian Peninsula. For its survival, the species needs to become a parasite of one of the two species of the Myrmica ant genus: M. rubra or M. scabrinodis, in whose nests it completes its life cycle. It also needs the presence of the larval host plant, Sanguisorba officinalis. Using the known distribution of P. nausithous in 10 × 10 km UTM squares, we work out the potential distribution of the species and the effect of climate change, using two different scenarios (SRES A2 and B2, which respectively predict 3.4 and 2.4 °C of temperature increase), by modulating it based on the species on which it depends for survival. The obtained models present AUC values (Area Under a Receiver Operating Characteristic—ROC-Curve) above 0.9 in the case of P. nausithous and S. officinalis, and above 0.8 in the case of the host ants, indicating acceptable models. Climatic models show a reduction of the potential distribution area of P. nausithous with both climatic scenarios, and predict as favourable areas in 2080 locations where the species is currently not found, but with presence of its host plant and ants. If this process takes place, an introduction in its favourable areas in the Pyrenees could be considered in order to conserve the species in the future.