1. Institute of Freshwater ResearchNational Board of Fisheries, 178 93, Drottningholm, Sweden
2. Population Biology/Department of Ecology and Evolution, Evolutionary Biology Centre (EBC), Uppsala University, Norbyvägen 18D, 752 36 Uppsala, Sweden
3. Laboratory of Aquatic Ecology, Katholieke Universiteit Leuven, Charles de Bériotstraat 32, 3000 Leuven, Belgium
4. Department of Zoology, Stockholm University, 106 91 Stockholm, Sweden