1. Centre for Biodiversity Theory and Modelling, Theoretical and Experimental Ecology Station, CNRS and Paul Sabatier University, 09200 Moulis, France
2. Department of Mathematics, The University of Arizona, 617 North Santa Rita Avenue, Tucson, AZ 85721, USA
3. Department of Environment and Society, Utah State University, 5215 Old Main Hill, Logan, UT 84322, USA