Vacant niche in alpine habitat: the case of an introduced population of the butterfly Erebia epiphron in the Krkonoše Mountains

Abstract A vacant niche in alpine habitats of the Krkonose Mts. (Western Sudetes, Czech Republic) was colonised by a non-native butterfly Erebia epiphron (Lepidoptera: Nymphalidae, Satyrinae) as a result of artificial introduction of 50 females in 1932 and 1933. The species established a large population occupying an entire area above the timberline on one of parallel ridges (East) of the mountains, but it has not yet colonised the parallel Western ridge, which is almost identical in area, altitude and vegetation. We compared altitudinal distribution and adult habitats of the alien species and of its native congener, E. euryale. Distribution of both species was significantly affected by altitude, but habitat type predicted butterfly numbers better than altitude in regression models. The introduced species was sympatric with the native one near the timberline, but its altitudinal optimum was higher, within tundra grasslands, where the native E. euryale did not occur. Peak adult emergence of E. euryale was later than in E. epiphron and followed identical pattern in allopatry. The failure of E. epiphron to colonise the Western ridge is attributable to its incapability to disperse across wooded areas. The Krkonose alpine communities are unsaturated with species, which is striking in comparison with native butterfly fauna of lower Hrubý Jesenik Mts. We interpret this by a past encroachment of alpine grasslands in the Krkonose Mts. by the dwarf pine Pinus mugo.