1. Department of Biology, Dalhousie University, Halifax, NS, Canada B3H 4J1.
2. Department of Economics and Finance, University of Wyoming, Laramie, WY 82071, USA.
3. Plymouth Marine Laboratory, Plymouth PL1 3DH, UK.
4. Virginia Institute of Marine Sciences, Gloucester Point, VA 23062–1346, USA.
5. Department of Systems Ecology, Stockholm University, Stockholm, SE-106 91 Sweden.