1. L. W. Botsford is in Department of Wildlife, Fish, and Conservation Biology, Center for Population Biology, University of California, Davis, CA 95616, USA. J. C. Castilla is in Departamento de Ecologia, Facultad de Ciencias Biologicas, Pontificia Universidad Catolica de Chile, Casilla 114-D, Santiago, Chile. C. H. Peterson is at University of North Carolina at Chapel Hill, Institute of Marine Sciences, Morehead City, NC 28557, USA.