1. Department of Aquatic Ecology and Ecotoxicology, Faculty of Science, University of Amsterdam, P.O. Box 94084, 1090 GB Amsterdam, The Netherlands, Department of Theoretical Biology, Faculty of Earth and Life Sciences, and Department of Animal Ecology, Institute of Ecological Science, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands, and Department of Chemistry and Ecotoxicology, Institute for Inland Water Management and Waste Water Treatment (RIZA), P.O. Box 17, 8200 AA Lelystad,...