Better up, worse down: Bidirectional consequences of three decades of climate change on a relict population of Erebia cassioides

Orophilous species are often unable to escape theconsequences of climate change because mountains aresurrounded by unsuitable habitats. Among them, severalendemic species belonging to the genus Erebia Dalman(Lepidoptera, Nymphalidae, Satyrinae) can be considered askey species to assess the risk of biodiversity loss of mountainhabitats. The aim of this paper is to measure changes thathave occurred in the altitudinal distribution of Erebia cassioideson the Pollino Massif (Southern Italy) during the last37 years. Sixteen sites sampled in 1975 have been resampledafter about three decades (2004, 2012). In 1975 56 % of thesampled population inhabited sites above and 44 % sitesbelow the treeline, while in 2004 and 2012 99 % of thepopulation were observed above the treeline. Furthermore,we observed an uphill shift of 180 m in the barycentre altitudeof the species distribution and an unexpected increaseddensity of the population above the treeline which led to arange reduction coupled to population increase of E. cassioides.This pattern contrasts with the usually observed one thatcouples habitat reduction to population decreasing. Thereason for the observed pattern is unclear, but the implicationfor conservation strategies could be important if confirmedfor other species. In fact, during coming decades localextinctions as a consequence of climate change might befewer and more delayed than expected, and relict populations of cold adapted species could be preserved for a longer timespan within optimal habitat refugia.