Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France.|Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France.|Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France.|Decision and Bayesian Computation, Pasteur Institute, CNRS UMR 3571, 25-28 rue du Dr Roux, 75015 Paris, France.|Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France.