1. Department of Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada.
2. Department of Environmental Sciences, P.O. Box 65, Fl-00014 University of Helsinki, Helsinki, Finland.
3. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Bioscience, University of Oslo, NO-0316 Oslo, Norway.
4. Department of Natural Sciences, Faculty of Engineering and Science, University of Agder, P.O. Box 422, 4604 Kristiansand, Norway.