1. J. T. Wootton, Department of Ecology and Evolution, University of Chicago, 1101 East 57 Street, Chicago, IL 60637, USA.
2. M. S. Parker, Department of Biology, Southern Oregon State College, Ashland, OR 97520, USA.
3. M. E. Power, Department of Integrative Biology, University of California, Berkeley, CA 94720, USA.