Domingo Alcaraz-Segura University of Buenos Aires and CONICET Laboratory of Regional Analysis and Remote Sensing Av. San Martín 4453 1417 Buenos Aires Argentina Phone: +54 11 4524-8070 (Ext. 8109) Fax:     +54 11 4514-8730 University of Almería Department of Ecology and Plant Biology Crta. Sacramento s/n. 04120 La Cañada de San Urbano, Almería Spain Phone: +34 950 01 5958 Fax:     +34 950 01 5069 e-mail: dalcaraz at ual.es