Acknowledgements
AC Espinosa was a recipient of a graduate student fellowship from the Consejo
Nacional de Ciencia y Tecnología (CONACyT, México). The authors
would like to acknowledge the support of the Consejo Nacional de Ciencia
y Tecnología (CONACyT, México) in enabling them to carry out project
32505-T from 1999-2001, and the Dirección de Asuntos del Personal
Académico of the Universidad Nacional Autónoma de México (UNAM) for
financial support with grant IN-219303 from 2003-2005. We also wish to
thank P Islas, P Cisneros, and J Aguilar for their invaluable help in the field
and laboratory work.