1. Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
2. Present address: Department of Environmental Sciences, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia
3. Arnold Arboretum, Harvard University, Cambridge, MA 02138, USA
4. Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
5. Department of Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637, USA
6. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA