[1] WSL Swiss Fed Res Inst, CH-8903 Birmensdorf, Switzerland
[2] ETH, Dept Environm Sci, CH-8092 Zurich, Switzerland
[3] Univ Aix Marseille 1, Lab Populat Environm Dev, UMR 151, UP IRD, F-13331 Marseille 03, France
[4] Univ Grenoble 1, Lab Ecol Alpine LECA, CNRS, UMR 5553, F-38041 Grenoble 09, France