1. University of Fribourg, Unit of Ecology & Evolution, ch. du Musée 10, CH-1700 Fribourg, Switzerland. E-mail: ; g.blandenier@bluewin.ch
2. Integrative Ecology Group, Estación Biológica de Doñana (EBD-CSIC), C/Américo Vespucio s/n, 41092, Sevilla, Spain