Jianguo Liu is in the Center for Systems Integration and Sustainability, Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan 48824, USA. He is also guest professor at the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, and specially appointed professor, Fudan University, Shanghai, China. e-mail: [email protected]
Jared Diamond is in the Department of Geography, Bunche Hall, University of California, Los Angeles, California 90095-1524, USA. e-mail: [email protected]
Supplementary information accompanies the paper on www.nature.com/nature.
