Isolated mountains of the temperate zone that overtop the timberline in their highest altitudes offer several advantages for studying the biology of alpine relics. In Europe, the subalpine summit habitats of the "middle high mountains" (Jenik 1998) include the uplands of Northern England and Scotland, the French Massive Central, and the highest parts of the Hercynnian system in France (Vosges), Germany (Harz, Schwarzwald, Bayerischer Wald), and the Sudeten Mountains at the Czech/Polish border region (Krkonose Mts. in the West, Kralicky Sneznik and Jesenik Mts. in the East). Due to their small extents of (sub)alpine habitats, studies on alpine relics occurring in such systems can address questions that would not be tractable in the much larger and considerably higher systems of the Alps, Carpathians, or Pyrenees. In particular, the low richness of alpine elements in these small mountain areas reduces the complexity of biotic interactions, their small total areas facilitate research, and the geographic isolation from other mountain systems ensures that local populations do not interact with conspecific populations elsewhere. Relic species inhabiting middle high mountains are particularly vulnerable to habitat loss, aggravated by the ongoing climate change (Hill et al. 2002; Franco et al. 2006).
High mountain insects are subject to ecophysiological constraints, confining their distributions to high altitudes (Hodkinson 2005). Assuming that the outcome of warming climate results in a vertical shift in vegetation belts (e.g., Kullman 2006; Jurasinski and Kreyling 2007), alpine relics occurring above the timberline can be threatened in two ways, either directly by a shift of climatic conditions beyond their physiological limits, or indirectly, via habitat loss (e.g., Grabherr 2003; Holten 2003; Virtanen 2003; Virtanen et al. 2003). Either way, they should respond by uphill shifts and tracking of suitable climate conditions (e.g., Hill et al. 2002; Konvicka et al. 2003; Wilson et al. 2007) and these displacements will eventually hit the upper limits in mountains not high enough to accommodate all the species occurring there now. Still, there had been other periods of relatively warm climate during the Holocene, especially the Atlanticum when the temperature was 1-2 degrees warmer than at present (Prentice et al. 2000), and there is little doubt that all the Northern and alpine relics occurring in European middle high mountains survived these warmer periods in situ, within the mountains where they occur today.
Two relic butterflies inhabit the highest altitudes of the Sudeten mountains: Erebia epiphron (Knoch, 1783) and E. sudetica Staudinger, 1851 (both Nymphalidae: Satyrinae). Taxonomists treat these populations as an endemic subspecies, E. epiphron silesiana (Meyer et Dür, 1852) and E. s. sudetica Staudinger, 1851, both belonging to species with considerably wider distributions elsewhere. Therefore, the Sudeten subspecies display extremely restricted native ranges: Exclusively the Jesenik Mts. in the case of E. epiphron and Jesenik Mts., Rychlebske Mts. and Kralicky Sneznik Mts. in the case of E. sudetica (Kuras et al. 2001c). An artificially established population of E. epiphron occurs in the Krkonose Mts., Western Sudetens. The closest native populations of the two species occur 200 km apart in the Carpathian High Tatras,
Slovakia (E. epiphron) and 600 and 800 km apart in the Rodna Mts., Eastern Carpathians, Romania and Grindelwald, Berner Oberland, Switzerland, respectively (E. sudetica).
Butterflies with such a restricted distribution have long attracted the attention of lepidopterists (e.g., Schwarz 1948; Stiova 1988). A systematic investigation of their ecology, however, began as late as the mid-1990s, when T. Kuras and J. Benes, then from Palacky Univerisity, Olomouc, initiated their mark-recapture surveys. This gradually extended to studies of behavior and population genetics, and to collecting additional information on the ecology of E. euryale (Esper, 1805) and E. ligea (Linnaeus, 1758), two Erebia species inhabiting the Sudeten mountain forests. Inclusion of E. sudetica to the EU Habitat Directive recently inspired annual monitoring of its sites. At present, Sudeten Erebia is among the most thoroughly studied butterflies in Central Europe.
Here, we review the ecological information available to date, focusing on the prospects of populations vis a vis recent climate change. We document that the population structure of E. epiphron and E. sudetica depends on the spatial distribution of their habitats. We then describe the outcomes of a notable experimental release of E. epiphron to the previously unoccupied Krkonose Mts., conducted in the 1930s. Recent surveys of the Krkonose population revealed that under certain conditions, this alpine butterfly can colonize altitudes below its subalpine habitats, and the same applies for E. sudetica, which occurs in large numbers at damp openings within the forest belt of Jesenik Mts. These observations suggest that although there exist ecophysiological limits to down-slope distribution of both species, their current distribution within the Sudeten system depends more on habitat availability than on climate.
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