1. Desert Ecology Research Group; School of Biological Sciences; University of Sydney; Sydney NSW 2006 Australia
2. Trophic Cascades Program; Department of Forest Ecosystems and Society; Oregon State University; Corvallis OR 97331 USA
3. School of Environmental and Forest Sciences; University of Washington; Seattle WA 98195 USA
4. CSIRO Land and Water Flagship; PO Box 2111 Alice Springs NT 0871 Australia