1. Department of Evolutionary Biology and Environmental Studies; University of Zurich; Winterthurerstrasse 190 CH-8057 Zürich Switzerland
2. Department of Aquatic Ecology; Eawag: Swiss Federal Institute of Aquatic Science and Technology; Überlandstrasse 133 CH-8600 Dübendorf Switzerland
3. National Center for Ecological Analysis and Synthesis; University of California, Santa Barbara; 735 State Street, Suite 300 Santa Barbara CA 93101-5504 USA