Ecological Limits Vis-à-vis changing climate: Relic Erebia butterflies in insular Sudeten mountains

Abstract

Insular middle mountains of Central Europe, such as Jesenik Mts. (max. altitude 1,495 m) and Krkonose Mts. (1,602 m), both in the Sudeten system, are poor in relic species, but the relic populations are suitable for studying the population responses to recent climatic change. There are two relic butterflies that are native to Jesenik Mts., each traditionally classified as an endemic subspecies: Erebia sudetica sudetica (Staudinger, 1851), a species protected by the EU Habitat Directive, and E. epiphron silesiana Meyer & Dür, 1852. Whereas Jesenik E. epiphron forms continuous populations, restricted to summit Nardus-dominated grasslands and not entering forested elevations, the distribution of Jesenik E. sudetica forms an archipelago at wet timberline sites and at clearings within mountain forests. Although both species avoid mountain forests, their lower distribution limits seem to be mediated by a limited range of available habitats, rather than of direct ecophysiological constraints. A non-native population of E. epiphron in Krkonose, transferred from the Jesenik in the 1930s, descends to ca 1,100 m, colonizing large clearings with cultural hay meadows within the forest belt. There is also behavioral and molecular evidence that E. epiphron cannot disperse through continuous forest. On the other hand, E. sudetica has a better dispersal power, and recent monitoring of its native Jesenik distribution suggests active colonization of woodland clearings. Thus, both butterflies can survive an altitudinal increase of the timberline, provided open habitats within the forests are secured. This conjecture suggests that these two and other alpine species survived past warmer periods of the Holocene in mountains, such as Jesenik owing to disturbance dynamics that never allowed complete forest closure. In the higher Krkonose, in contrast, they probably lacked suitable open habitats because of the encroachment of such sites by Pinus mugo dwarf pine, which is native to Krkonose but non-native to Jesenik.