1. Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN 55108, USA;
2. Environmental Studies Program, Dartmouth College, Hanover, NH 03755, USA;
3. (present address) Division of Biology, Kansas State University, Manhattan, KS 66506, USA;
4. Department of Botany, University of Cape Town, Cape Town, South Africa;
5. Centre for Ecosystem Management, Edith Cowan University, Perth, Western Australia, Australia