[1] Univ London Imperial Coll Sci Technol & Med, Ctr Populat Biol, Dept Biol, Ascot SL5 7PY, Berks, England
[2] Univ London Imperial Coll Sci Technol & Med, Ctr Populat Biol, Nat Environm Res Council, Ascot SL5 7PY, Berks, England
[3] Univ Calif Berkeley, Dept Integrat Biol, Berkeley, CA 94720 USA