1. CNRS UMR5023, Ecologie des Hydrosystèmes Fluviaux, Université Lyon 1, 69622 Villeurbanne Cedex, France;,
2. Departament d'Ecologia, Universitat de Barcelona, 08028 Barcelona, Spain;
3. Department of Environmental Science, Policy & Management, University of California, Berkeley, California 94720-3112;