1. Spatial Ecology Department, the Netherlands Institute of Ecology (NIOO-KNAW), Post Office Box 140, 4400 AC Yerseke, Netherlands.
2. School of Ocean Sciences, University of Wales Bangor, Askew Street, Menai Bridge LL59 5AB, UK.
3. Centre de Recherches sur la Cognition Animale, CNRS UMR 5169, Universite Paul Sabatier 118, Route de Narbonne, 31062 Toulouse Cedex 04, France.
4. Department of Environmental Sciences, Copernicus Institute, Utrecht University, Post Office Box 80115, 3508 TC Utrecht, Netherlands.
5. Aquatic Food Webs Department, Netherlands Institute of Ecology, Rijksstraatweg 6, 3631 AC, Nieuwersluis, Netherlands.