1. Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280
2. Department of Biology, University of Rochester, Rochester, New York 14627-0211
3. Göttingen Campus Institute for Dynamics of Biological Networks, Georg August University, 37075 Göttingen, Germany
4. Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany
5. Max Planck Institute for Multidisciplinary Sciences, 37075 Göttingen, Germany
6. Institute for Dynamics of Complex Systems, Georg August University, 37077 Göttingen, Germany
7. Department of Biology, Philipps University, 35043 Marburg, Germany
8. School of Mathematics and Statistics and Bateson Centre, University of Sheffield, Sheffield S10 2TN, United Kingdom