1. Department of Integrative Biology University of California Berkeley CA 94720 USA
2. Department of Biology Tufts University Medford MA 02115 USA
3. Center for the Ecology of Infectious Diseases University of Georgia Athens GA 30602 USA
4. University of California Berkeley CA 94720 USA
5. Centre for Ecology and Conservation, College of Life and Environmental Sciences University of Exeter Penryn Campus Penryn TR10 9FE UK