We are grateful to Bruce S. Lieberman and Jill Hardesty for evaluation of an earlier version of our manuscript. Our research was made possible by grants from the National Science Foundation to The University of Kansas (BSR-9024567 and DEB-9505100), a bridging-fund grant from The University of Kansas, the R. C. and Lillian B. Moore funds administered by the Kansas University Endowment Association, and the generous support of Russell M. Jeffords.