Ground-Living Spider Communities (Araneae) on Boreal and Hemiboreal Peatbogs
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Ground-living spider communities (Araneae) on boreal and hemiboreal peatbogs Seppo Koponen Zoological Museum, Centre for Biodiversity University of Turku, FIN-20014 Turku Finland; e-mail: [email protected] Introduction Peatbogs are typical biotopes in the northern coniferous forest zone. Approximately a third of the land area of Finland was covered by peatlands, of which about a half has been drained for forestry, farming and peat harvesting (Wahlström et al. 1996). So peat- land ecosystems (mires, bogs, fens) are endangered even in northern Europe, and many organisms living in peatland habitats are nowadays considered as threatened. This is true also for spiders (e.g. Koponen 1985). For example, in the recent Finnish Red Data Book (Rassi et al. 2000) six of the total 34 listed spider species are inhabitants of mires. Some general information is here given on typical peatbogs spiders, both abundant and rare ones, and on their distributional trends, along a transect from the southern- most parts of the hemiboreal vegetation zone to northern borders of the northern boreal zone. Material Spiders were collected along a transect from southern Lithuania (54°N) to Lapland (northern Finland, 69°30’N). Peatbogs studied included both open treeless and pine growing Sphagnum bogs in the hemiboreal and boreal vegetation zones. Ground-li- ving, epigeic spiders were collected using pitfall traps. For details of study sites and collecting methods, see Koponen et al. (2001). Additional data used here is based on studies by Asta Vilbaste on Estonian peatbogs (e.g. Vilbaste 1980-81) and on the pre- sent author’s published (Koponen 1968, 1979a, 1979b, 1985, Lehtinen et al. 1979) and unpublished works in Finland. Abundant species Some typical and abundant peatbog species occurred more or less regularly on bogs along the whole transect from Lithuania to Lapland. This group of widely distributed spiders included Pardosa sphagnicola, Agyneta cauta, Centromerus arcanus, Lepthyphantes angulatus, Meioneta mossica, Cnephalocotes obscurus, Pocadicnemis pumila, and Walckenaeria nudipalpis. ○○○○○○○○○○○○○○○○○○○○○ 212 ○○○○○○○○○○○○○○○○○○○○○○○○○○ The Finnish Environment 485 Dominant species on Lithuanian peatbogs were Aulonia albimana, Pardosa sphagni- cola, Pirata uliginosus, Scotina palliardi, Centromerus arcanus, and Trochosa spinipalpis. Do- minants in southern Finland were Arctosa alpigena, Pardosa hyperborea, P. sphagnicola, Alopecosa pulverulenta, Antistea elegans, and Agyneta cauta. Dominant species on peatbogs in central Finland included Pardosa sphagnicola, P. hyperborea, Arctosa alpigena, Agyneta cauta, and A. decora. The following species dominated in northern Finland: Pardosa hyperborea, P. atrata, Arctosa alpigena, Pelecopsis mengei, Hilaira nubigena, and H. herniosa. The great majority of abundant and typical peatbog spiders belonged to two fa- milies: Lycosidae (wolf spiders; e.g. genera Pardosa, Pirata, Trochosa, Aulonia, and Arctosa) and Linyphiidae (money spiders; e.g. Agyneta, Centromerus, Lepthyphantes, Meioneta, Hilaira, and Walckenaeria). Rare species Six mire-living spiders have been included in the recent Finnish Red Data Book (Rassi et al. 2000): Emblyna brevidens, Ceraticelus bulbosus, Mecynargus (sub Rhaebothorax) fovea- tus, Satilatlas britteni, Ozyptila gertschi, and Zora parallela. Most of them were found at the present study localities. The small-sized linyphiid Ceraticelus bulbosus has an interesting range; it is widely-distributed in North America, spread throughout Siberia but known in Europe only from Kuusamo in Finland and from a few localities in Central Europe. Also other spiders which are not included in the Finnish Red Data Book but considered rare in northern Europe were found on the studied peatbogs (Table 1). These species are typical of mires, although some of them can be found also in other type of habitats. Table 1. Examples of rare bog spiders; species of the Finnish Red Data Book are excluded. Species Family General range in northern Europe Centromerus unidentatus Linyphiidae southern C. incultus Linyphiidae southern Minicia marginella Linyphiidae southern Taranucnus setosus Linyphiidae southern Lepthyphantes ericaeus Linyphiidae southern Carorita limnaea Linyphiidae southern Glyphesis cottonae Linyphiidae southern Agyneta suecica Linyphiidae ? Agyneta breviceps Linyphiidae northern Semljicola angulatus Linyphiidae northern Wabasso questio Linyphiidae northern Dipoena prona Theridiidae southern Pardosa maisa Lycosidae northern? Neon valentulus Salticidae southern Agroeca dentigera Liocranidae southern Drassyllus pusillus Gnaphosidae southern Distributional patterns Spiders living on the studied hemiboreal-boreal peatbogs can be roughly divided into three groups: widely-distributed (see above), southern and northern species (cf. also Koponen et al. 2001). ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ The Finnish Environment 485 ○○○○○○○○○○○ 213 Of the southern species, Aulonia albimana was found only on Lithuanian peatbogs where it was the most dominant species; it is not known in Estonia (Vilbaste 1987) but in Finland it is rarely collected in dry places, not on bogs (e.g. Lehtinen et al. 1979). Phrurolithus minimus, a southern bog species in Lithuania, is known from a stony shore in Estonia (Vilbaste 1987) but not found in Finland. The following bog species with a southern general range were found as far north as in southern Finland: Drassyllus lute- tianus, Zelotes latreillei, Maro minutus, Sintula corniger, and Walckenaeria nodosa; and some species reach their northern limit in central Finland: Pirata insularis, P. uliginosus, Pelecop- sis parallela, and Meioneta affinis. Of the northern species, e.g. Gnaphosa orites and Semljicola lapponicus were found only in northern Lapland, Hilaira nubigena and Walckenaeria karpinskii also in central Finland, and Gnaphosa lapponum and Mecynargus sphagnicola even in southern Finland. The known southern limit of Pardosa atrata, Latithorax faustus and Robertus lyrifer is in Estonia (Vilbaste 1980-81) and the range of Gnaphosa microps, Pardosa hyperborea and Arctosa alpigena extends to Lithuanian peatbogs. Conclusion Typical peatbog spiders belong especially to the families Linyphiidae, Lycosidae and Gnaphosidae. Clear differences were found in communities at different latitudes. In general, faunas found in the hemiboreal zone (from Lithuania to southernmost Fin- land) resembled each others. However, some marked differences were found between sites in the hemiboreal zone, the most striking one was the absence of the dominant species of Lithuanian bogs, Aulonia albimana, both on Estonian and Finnish peatbogs. The assemblage of abundant species on boreal (Finnish) peabogs also showed geo- graphical differences, especially the northern boreal bog sites differed from the middle and southern boreal ones. For example, Hilaira species and Pelecopsis mengei were typi- cal of the northern boreal, and P. parallela and Pirata uliginosus of middle and southern boreal peatbogs. Marked number of threatened and other rare spider species was found on peatbogs. This indicates the importance of protecting remaining mire habitats, es- pecially in areas where natural bogs are scattered. Acknowledgements I wish to thank Vygandas Relys (Vilnius University, Lithuania) for co-operation and valuable information. References Koponen, S. 1968: Über die Evertebrata-Fauna (Mollusca, Chilopoda, Phalangida, Araneae und Coleoptera) von Hochmooren in Südwest-Häme. – Lounais-Hämeen Luonto 29: 12-22. Koponen 1979a: Differences of spider fauna in natural and man-made habitats in a raised bog. – Use of Ecol. Variables in Environmental Monitoring, Nation. Swedish Envir. Prot. Board, Rep. PM 1151: 104-108. Koponen, S. 1979b: Kuusamon soiden hämähäkkilajistosta (Summary: On the spider fauna of mi- res in Kuusamo). – Acta Univ. Ouluensis A 68, Biol. 4: 209-214. Koponen, S. 1985: Soiden hämähäkkilajiston muutoksista (Summary: On changes in the spider fauna of bogs). – Mem. Soc. Fauna Flora Fennica 61: 19-22. Figure ○○○○○○○○○○○○○○○○○○○○○ 214 ○○○○○○○○○○○○○○○○○○○○○○○○○○ The Finnish Environment 485 Koponen, S., Relys, V. & Dapkus, D. 2001: Changes in structure of ground-living spider (Araneae) communities on peatbogs along a transect from Lithuania to Lapland. – Norw. J. Entomol. 48 (in press). Lehtinen, P.T., Koponen, S. & Saaristo, M. 1979: Studies on the spider fauna of the southwestern ar- chipelago of Finland II. The Aland mainland and the island of Eckerö. – Memoranda Soc. Fauna Flora Fenn. 55: 33-52. Rassi, P., Alanen, A., Kanerva, T. & Mannerkoski, I. (toim.) 2000: Suomen lajien uhanalaisuus 2000. – Ympäristöministeriö, Helsinki, 432 s. Uhanalaisten lajien II seurantatyöryhmä, esipainos [ http://www.vyh.fi/luosuo/lumo/lasu/uhanal/uhanal.htm, 23.10.2000]. Vilbaste, A. 1980-81: The spider fauna of Estonian mires. – ENSV TA Toim. Biol. 29, 313-327 and 30, 7-17. Vilbaste, A. 1987: Eesti ämblikud (Aranei). - Valgus, Tallinn, 114 pp + 512 maps. Wahlström, E., Hallanaro, E-L. & Manninen, S. 1996: The future of the Finnish Environment. – Edita, Helsinki, 272 pp. ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ The Finnish Environment 485 ○○○○○○○○○○○ 215.