1. Department of Zoology, University of Western Ontario, London, Ontario, Canada N6A 5B7
2. Cooperative Research Centre for Freshwater Ecology, University of Canberra, Belconnen, ACT 2601, Australia
3. Canada Centre for Inland Waters, 867 Lakeshore Rd, P.O. Box 5050, Burlington, Ontario, Canada L7R 4A6