1. Department of Biology, Centre for Biodiversity Dynamics; Norwegian University of Science and Technology; NO-7491 Trondheim Norway
2. Department of Ecology and Genetics/Animal Ecology; Uppsala University; SE-752 36 Uppsala Sweden
3. Department of Evolutionary Ecology; Max Planck Institute for Evolutionary Biology; 24306 Plön Germany
4. University of Gotland; SE-621 67 Visby Sweden