1. Department of Ecology and Evolutionary Biology, University of California Irvine, California 92697, USA; Present address: Department of Biological Sciences, University of Cincinnati, 614 Rieveschl Hall, Cincinnati, OH 45221‐0006 USA,
2. Present address: River Basin Research Center, Gifu University, Yanagido 1‐1, Gifu 501‐1193, Japan