[1] Univ Cambridge, Dept Zool, Downing St, Cambridge CB2 3EJ, England
[2] Univ Vermont, Gund Inst Environm, Rubenstein Sch Environm & Nat Resources, Environm Program, Burlington, VT 05405 USA
[3] UCL, Ctr Biodivers & Environm Res, Medawar Bldg, London WC1E 6BT, England
[4] Princeton Univ, Woodrow Wilson Sch Publ & Int Affairs, Princeton, NJ 08544 USA
[5] Univ Exeter, Sch Business, Land Environm Econ & Policy Inst, Prince Wales Rd, Exeter EX4 4PJ, Devon, England