[1] Univ Toronto, Dept Ecol & Evolutionary Biol, Toronto, ON M5S 3B2, Canada
[2] CNRS, Ctr Ecol Fonct & Evolut, F-34293 Montpellier 05, France
[3] ETH, Swiss Fed Inst Technol, Dept Environm Sci, Inst Terr Ecosyst, CH-8092 Zurich, Switzerland
[4] Goethe Univ Frankfurt, Inst Phys Geog, D-60438 Frankfurt, Germany