[1] CNRS, Ctr Biodivers Theory & Modelling, Theoret & Expt Ecol Stn, F-09200 Moulis, France
[2] Paul Sabatier Univ, F-09200 Moulis, France
[3] Univ Arizona, Dept Math, 617 North Santa Rita Ave, Tucson, AZ 85721 USA
[4] Utah State Univ, Dept Environm & Soc, 5215 Old Main Hill, Logan, UT 84322 USA