1. Department of Biology, Hampden-Sydney College, Hampden-Sydney VA 23943, USA
2. Department of Evolutionary Biology, Ecology, and Environmental Science, University of Barcelona, 08028 Barcelona Spain
3. Department of Ecology & Evolutionary Biology, Brown University, Providence RI 02912, USA; current address Department of Biology, West Chester University, West Chester PA 19383, USA
4. Biology Department, Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA
5. Department of Wildlife Management, North Slope Borough, Barrow AK 99723, USA
6. Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks AK 99775, USA