1. Department of Biological Sciences, Dartmouth College, 78 College St., Hanover, New Hampshire 03755 USA
2. Department of Biology, 221 Morrill Science Center South, 611 N. Pleasant St., University of Massachusetts, Amherst, Massachusetts 01003 USA
3. Department of Applied Ecology, Campus Box 7617, North Carolina State University, Raleigh, North Carolina 27695 USA