Climate Influence on the Adult Phengaris alcon Abundance in the Alvão Natural Park, Northern Portugal

Phengaris alcon is one of Europe’s emblematic invertebrate species and is currently classified as Near Threatened on the IUCN Red List. In Portugal, this endangered species occurs mainly in Alvão Natural Park (ANP). This study investigated the effects of microclimatic conditions on the adult P. alcon capture records in the Libânia meadow of the ANP. Adult butterflies were monitored (Mark–release–recapture method) from 2006 to 2014 (except 2012). Microclimatic conditions were modelled (NicheMapR), generating values of precipitation (Prec), maximum (Tmax), minimum (Tmin) and mean temperature (Tmean), solar radiation (SR), relative humidity (RH), soil surface wetness (PCTWET), and wind speed (WS). Growing degree days (GDD), cumulative precipitation (Prec-cum), and seven-day means (d7) for all variables were calculated. Seven microclimatic variables showed strong associations with adult abundance. Higher values of Prec-cum, Tmin-d7 and Prec-d7 were negatively associated with abundance, whereas higher values of SR, RH-d7, Tmean-d7 and PCTWET-d7 were significantly associated with butterfly abundance. More than 50% of individuals were recorded within the following favourable climatic ranges: Prec-cum = 157.9–251.4 mm; SR = 6730.1–8220.4 W/m2; Tmin-d7 = 8.0–12.2 °C; RH-d7 = 71.2–86.7%; Prec-d7 = 0.0–0.8 mm; Tmean-d7 = 13.2–18.0 °C; and PCTWET-d7 = 60.8–92.0%. These findings provide quantitative microclimatic ranges that could guide habitat management and support the long-term persistence of P. alcon under future climate change.