awarded to the author by the Direccion General de Asuntos del Personal Académico 
(Universidad Nacional Autonoma de México). I am indebted to the members of the Scholarship 
Committee at the Facultad de Ciencias (UNAM) for their support. I also thank the funding for 
field work I received from the International Center of Tropical Ecology, SigmaXi, and the 
Missouri Botanical Garden. 
Finally I want to thank all the members of my committee for the time they spent reading 
and making suggestions for the improving of my dissertation. Particularly I want to thank Dr. 
Henk van der Werff for his confidence, advises, and the discussions we had about my work. 
