Spiders ( Araneae ) of stony debris in North Bohemia

The arachnofauna was studied at five stony debris sites in northern Bohemia. In Central Europe, the northern and montane species inhabiting cold places live not only on mountain tops and peat bogs but also on the lower edges of boulder debris, where air streaming through the system of inner compartments gives rise to an exceedingly cold microclimate. At such cold sites, spiders can live either on bare stones (Bathyphantes simillimus, Wubanoides ura/ensis) , or in the rich layers of moss and lichen (Dip/oeentria bidentata). Kratoehviliella bieapitata exhibits a diplostenoecious occurrence in stony debris and on tree bark. Latithorax faustus and Theonoe minutissima display diplostenoecious occurrence in stony debris and on peat bogs. The occurrence of the species Seotina eelans in the Czech Republic was documented for the first time.


INTRODUCTION
Stony debris constitute, in Central Europe, island ecosystems which have remained virtually intact over the entire Holocene.Due to the unfeasibility of utilization, stony debris areas are among the few ecosystems that have only minimally been affected by man.In bulky accumulations, air can flow through the System of internal spaces.In this way, cold air can accumulate in the lower part of the talus, so that ice can form and persist there until late spring.This phenomenon, well known from the Alp region (FURRER 1 966), occurs widely in North Bohemia (KUBÄT 1971).Owing to the specific Substrate and microclimate, stony debris areas are inhabited by specific plant (SÄDLO & KOLBEK 1 994) and animal communitjes, contributing thus significantly to the biodiversity of the landscape (RUZICKA 1993a).We investigated spiders in five boulder accumulations in North Bohemia.

ITrapping
The spiders were trapped in modified pitfall traps made of rigid plastic.The traps contained a mixture of 7% formaldehyde and 1 0% glycerol with a few drops of a Surfactant (RUZICKA 1 982, 1 988).These traps were positioned 20 to 1 00 cm under the surface of stony debris.They were exposed for one year.The preserved catch was then processed in the laboratory.

Sites
KKamenec.The Kamenec hill near Stary Sachov, organism grid mapping quadrat 5252.The northern slope, which declines into the Plou nice river »/alley, hosts a basalt debris accumulation at an elevation of about 350 m. ^ir flows through a System of Underground compartments in a thick boulder !ayer.Whereas warm water vapour leaves the upper part of the boulderfield i n winter, cold air streams from the lower part of the field in spring and early 5 -iummerand ice forms there.Characteristic of this debris accumulation is an sxceedingly rieh moss cover of the stones.The arcto-alpine moss species G3ymnomitrion corallioides and the montane fern Cryptogramma crispa vere found at the lower edge of the accumulation.Kamenec is the lowest ying site where those species have been observed in the Czech Republic PUJMANOVÄ 1 988, 1 989).26 traps were positioned here from June 1 993 o July 1 995, predominantly on the surface with some of them located within * he debris.The surface ones were emptied approximately at monthly ,b t itervals.ve ate i6)i ;i!ic /lilesovka.Milesovka is the highest mountain of the Ceske Stredohori Mountains, organism grid mapping quadrat 5449.A närrow striß of fine 'honolite debris lies on the foot of the southwestern slope at an altitude of !bout 550 m, underthe Vyrf Skäly rocks.Six traps were positioned here from une 1 993 to July 1 994 within the debris.lüuchy Vrch.Suchy Vrch hill in the Luzicke Hory mountains, west of the larenice village, organism grid mapping quadrat 51 53.The whole northern Jope of the Suchy Vrch is covered by phonolite boulders.Under the top, at n elevation of roughly 620 m, is a minor boulder accumulation; the slope grown with a forest.At an elevation of 580 m is a pseudo-karst ice cave, vertical fissure in the compact phonolite 1-2 m wide and 29 m long.The eiling of the cave is formed by stone blocks which are part of the stone accumulation (KRÄL & REZÄC 1 950).Cold air streams among blocks into the cave and causes ice formation there, particularly during the spring thawing.This is the only cave in the Czech Republic where ice persists all the year round (HROMAS 1 971 ). 1 2 traps were positioned within bare and forested debris and in the cave from June 1993 to July 1994.Maly Stozec.The Maly Stozec hill, the Luzicke Hory Mountains, organism grid mapping quadrat 51 53.A phonolite boulder accumulation lies belowthe top rocks, at an elevation of about 600 m.Three traps were positioned here within the debris from September 1 993 to July 1 994.
Muchov.The Muchov hill lies atthe eastern edge of the ernä Studnice crest, south of the town of Tanvald, organism grid mapping quadrat 5257.An extensive granite block field lies at the northern to northeastern edge of the top of the hill, at an elevation of 700-750 m (VITEK 1987).
Five traps were positioned here within the debris from September 1 993 to July 1994.RESULTS AND COMMENTS ON SOME SPECIES 872 spiders representing 108 species were collected on five sites.Twelve species were detected at three sites at least; some of them (e.g.Rugathodes bellicosus, Lepthyphantes notabilis, Micrargus apertus) are regulär and exclusive inhabitants of stony debris.The species richness of spider communities living in stony debris was confirmed again, as was the I differentiation of the species locationwith respectto the different microclimatic conditions existing atthe different sites of the stone accumulations (RUZICKA, Scotina celanswas found at the Kamenec hill at the forest edges of the upper part of the debris field: this is consistent with the data concerning this species published by GRIMM (1986).Although MILLER (1971) reported occurrence of this species in the former Czechoslovakia, he failed to specify the location.Thus the finding at the Kamenec site represents the only documented occurrence of Scotina celans in the Czech Republic.Latithorax faustus was observed in moss at the lower edge of the debris at the Kamenec hill.Until now, this northern species has only been known to inhabit peat bogs.Its occurrence has been reviewed by KURKA (1995) (1984) reported on the occurrence of this species on tree bark, CZAJKA (1971) found it in deep, shaded cracks in tree bark exposed to the north and, to a lesserextent, understones in the surroundings.Czech literature gives the following information on the environmental demands of this species: under stones sunk into loose forest litterfall under old pines and spruces (MILLER 1971), in leaf litter and under stones near a brook (BUCHAR & HAJER 1 990).In the Podyji National Park in Southern Moravia, specimens of Kratochviliella bicapitatawere observed in stony debris and in pseudokarst caves within a decaying gneiss massif (RÜ^lCKA 1 996).The fact that the spiders were found in stony debris on the Kamenec hill is a confirmation of the fact that this species inhabits stony biotopes (Fig. 1).FRANC & HANZELOVÄ (1 995) recordedKratochviliellabicapitata\n\he Underground spaces of a basalt block accumulation in the Cerovä Vrchovina highland in Southern Slovakia.
Diplocentria bidentata has only been found three times in the Czech Republic, viz. in moss at the lower edge of stony debris on the Plesivec hill in the Ceske StredohoTi Protected Landscape Area (BUCHAR 1989), in moss at the lower edge of an accumulation of sandstone rock blocks in the Teplicke Skäly within the Broumovsko Protected Landscape Area (RÜZlCKA 1 992), and in moss at the lower edge of the block debris in the Vydra river valley in the Sumava National Park (RÜ2ICKA in press).At the Kamenec hill, specimens of this spider were caught in pitfall traps laid in moss between boulders at the lower edge of the debris (Fig. 1 ).
Bathyphantes simillimus is an exclusive lithobiont, whose occurrence has been reviewed by RUZICKA (1994).Since then, specimens of this spider have been observed in the Harz Mountains (Igt.P. Sacher).At the Kamenec hill, this species was found both atthe lower edge of the debris and within the inner space at a depth of approximately 2 m.At the Suchy Vrch hill, it was found within the debris and in the ice cave.At the Muchov site, it was found within the debris.
Wubanoides uralensis was found at the Kamenec and Muchov sites within the debris, between bare stones.Although stony debris in the Czech Republic has been examined rather extensively (RUZICKA 1993b), this species has only been found at the northernmost sites (Fig. 1 ), only several tens of kilometers from the boundary of the maximum extent of the northern Pleistocene glacier (Fig. 1 ).A review of the overall occurrence of the species W. uralensis has been presented by RÜ^IÖKA & ZACHARDA (1994).

CONCLUSIONS
The occurrence in central Europe of northern species, living in cold places, is known from two climatically cold types of sites, viz.high mountain sites and peat bogs.A third habitat is to be added to those two, viz.lower edges of stony debris with a dynamic air Streaming regime, where places of exceedingly cold microclimate can be found even at lower elevations: although their area is very small, it is sufficient for the survival of prospering populations of invertebrates.
Not only the bare boulder surface but also moss and liehen layers form a suitable Substrate for habitation within the debris.Boulder surface can be inhabited, for instance, by the species Bathyphantes simillimus and Wubanoides uralensis, whereas the species Diplocentria bidentata has never been observed in bare stony formations although it can be found in moss layers at lower edges of cold stony debris.
The wet and cold environment of the inner space and lower edges of stony debris resembles the wet and cold environment of peat bogs.Diplostenoecious occurrence both on peat bogs and in stony debris has been ascertained for the species Theonoe minutissima and Latithorax faustus, whereas for the species Kratochviliella bicapitata, this type of occurrence is known on tree bark and also in stony biotopes.