Andrew Dobson is professor of ecology and evolutionary biology at Princeton University. His books include Conservation and Biodiversity. Robert D. Holt is Eminent Scholar and Arthur R. Marshall, Jr., Chair in Ecological Studies at the University of Florida. His books include Metacommunities. David Tilman is Regents Professor and McKnight Presidential Chair in Ecology at the University of Minnesota. His books include The Functional Consequences of Biodiversity (Princeton).