[1] CNRS, CEFE, F-34293 Montpellier, France
[2] Univ Calif Berkeley, Dept Environm Sci Policy & Management, Ecosyst Sci Div, Berkeley, CA 94720 USA
[3] Univ London Imperial Coll Sci Technol & Med, Dept Infect Dis Epidemiol, London W2 1PG, England
[4] Univ London Imperial Coll Sci Technol & Med, Div Biol, Ascot SL5 7PY, Berks, England