Exploring butterfly (Papilionoidea) diversity in the Circeo National Park (Latium, Italy) and its change in the last century

The global decline of insect pollinators, including butterflies, has raised significant concerns for biodiversity conservation. The main goal of this study is to develop a comprehensive approach for assessing butterfly fauna to be applied in different protected areas, using the Circeo National Park (CNP), Italy, as a model system. We integrated multiple data sources such as historical literature records, citizen science observations from iNaturalist, and systematic field sampling, to assess butterfly population trends, combining occurrence data with functional trait analyses and environmental change assessments. Fortnightly samplings were conducted across 18 transects representing the park’s main habitats (coastal dunes, agricultural areas, and promontory forests) from March to October over three consecutive years (2021–2023). Our findings document 70 butterfly species in total, including 5 species newly recorded for the Park and 42 species confirmed based on either field surveys or recent iNaturalist records, while 23 species remained unconfirmed. Using the Potential Extinction upon Time Series (PETS) index, we estimated a 16.7% potential extinction rate, substantially lower than previously inferred from literature-only data. Functional trait analyses revealed that climatic niche was the only trait significantly associated with species status, with thermally generalist species overrepresented among confirmed records. A significant record of temporal land-use changes emerged both within and around the park, including declining grasslands and forests, and increasing urbanization and intensive agriculture. Mean annual temperature increased by 3.2°C over 50 years (1973–2023), suggesting synergistic pressures from habitat fragmentation and climate warming. The complex interplay of habitat modification, fragmentation, and climate warming, particularly in the surrounding landscape of the park, appears to drive local species disappearances. Our dataset provides a baseline for investigating long-term ecological trends and informing conservation strategies in Mediterranean protected areas. We emphasize the need for continued monitoring in national parks and targeted conservation actions focusing on habitat connectivity and thermal refugia to support vulnerable butterfly populations.