1. Institut de Mathématiques de Bordeaux, UMR CNRS 5251 — Case 36, Université Victor Segalen Bordeaux 2, 3ter place de la Victoire 33000 Bordeaux Cedex, France
2. Laboratory of Ecotoxicology UPRES-EA 3222, IFRMP 23, University of Le Havre, 25 rue Philippe Lebon, 76058 Le Havre Cedex, France
3. Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
4. Department of Mathematics, Stevenson Center, Vanderbilt University, Nashville, TN 37240, USA