1. Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA
2. Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA
3. Cooperative Institute of Research in Environmental Science, Campus Box 216, University of Colorado, Boulder, CO 80309–0216, USA
4. Los Alamos National Laboratory, T–8 Mail Stop B285, Los Alamos, NM 87545, USA