A demographic and ecological study of an Italian population of Polyommatus ripartii: the ESU Polyommatus exuberans

Abstract: Polyommatus exuberans is an evolutionarily significant unit (ESU) of the lycaenid butterfly Polyommatus ripartii. This ESU is known to survive at only two sites in the Susa Valley (NW Italy). Lack of correct management, reforestation and frequent wildfires severely threaten this ESU (listed as endangered species in the most recent IUCN Italian Red List). Although the taxonomic rank of this taxon is still debated, current threats could cause extinction of its two remaining populations before its taxonomic rank and its ecology are clarified. We collected data for the first time on this population at the small site of Mompantero (ab. 10 ha). We used butterfly GPS-positioning and the mark-release-recapture (MRR)-method to estimate its population size (269 individuals), sex-ratio (1.36 M/F), lifespan (4.76 days), density (47/ha) and mobility (median 153 and 33 m for males and females, respectively). Both sexes are equally catchable. Catchability increases around midday and decreases during overcast weather. While the size and density of this small population are comparable to those of other endemic Polyommatus species (such as P. humedasae and P. gennargenti), scarce mobility makes its populations isolated and even more seriously threatened. Implications for insect conservation: We suggest that implementing an active management plan, including mowing before July and/or in autumn, and supporting ant diversity, is of immediate importance. Management should be extended to road verges, where the larval host plant (Onobrychis sp.) is abundant, and would thus also serve as corridors to favour dispersion between sites. Our research is the first study to investigate this taxon, thus shedding some light on the ecological and biological aspects that are crucial for long-term survival.