Centre d'Ecologie Fonctionnelle et Evolutive, Centre National de la Recherche Scientifique, 1919 Route de Mende, 34293 Montpellier Cedex 5, France, and Macroecology and Conservation Unit, University of Évora, Largo dos Colegiais, 7000–730 Portugal, email [email protected]
Paper submitted January 2, 2002; revised manuscript accepted January 24, 2002.
