Affiliation: | Botany Department, Duke University, Durham, North Carolina 27708, USA; School of the Environment, Duke University, Durham, North Carolina 27708, USA; Author for correspondence.; Present address: Department of Biology, West Virginia University, PO Box 6057, Brooks Hall, Morgantown, West Virginia 26506–6057, USA (fax +1 304 293 6363;e-mail;). |