1. Faculty of Science, Department of Ecosystem Biology, University of South Bohemia, Branišovská 31, 37005 České Budějovice, Czech Republic
2. Department of Environmental Science, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland
3. Institute of Biology, Komi Research Center, Urals Division, Russian Academy of Sciences, ul. Kommunisticheskaya 28, 167982 Syktyvkar, Russia