1. Centre d'Ecologie et Physiologie Energétique, CNRS, 23 Rue Becquerel, F-67087 Strasbourg Cedex 02, France
2. Department of Biology, Division of Zoology, University of Oslo, PO Box 1050 Blindern, NO–0316 Oslo, Norway
3. Norwegian Institute for Nature Research (NINA), Tungasletta 2, NO–7485 Trondheim, Norway