1. High Meadows Environmental Institute, Princeton University, Princeton, NJ 08544 USA.
2. Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520 USA.
3. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544 USA.
4. Department of Mathematics and Volen Centre for Complex Systems, Brandeis University, Waltham, MA 02453 USA.