Diversity, endemism and conservation of ferns (Polypodiales) in the Mexican Mountain Component

Abstract

We analyzed the distributional patterns of 95 selected species of leptosporangiate ferns inhabiting the Mexican Mountain Component, using grid-cells of one geographical degree as unit areas, applying endemism indices and richness and beta diversity analyses. Distributional data were obtained from several herbaria and specialized literature. Five grid-cells appear to be important for fern species richness, as they contain 35 to 49 species. These grid-cells are located in the Sierra Madre Oriental (SMO), Trans-Mexican Volcanic Belt (TMVB) and the Sierra Madre del Sur (SMS). Mean richness by latitudinal belts of one degree showed that the belts with highest values are related to the TMVB and SMS. A total of 13 grid-cells were recognized as important from the perspective of endemism; most of them are located also in the SMO, TMVB and SMS. The richest gridcells coincided with one of the main centres of endemism for ferns obtained in this study, located in the convergence of the southern part of the SMO, the eastern portion of the TMVB and the northern part of the SMS, reflecting the high humidity existing on the mountain slopes facing the Gulf of Mexico. Some important grid-cells recognized from richness and endemism analyses coincide with Mexican Natural Protected Areas. The beta diversity analysis showed a low degree of similarity among grid-cells, implying a high species replacement, as the result of environmental heterogeneity occurring in the Mexican mountain systems. On the other hand, the spatial analysis suggested a pattern of phytogeographical regionalization comprising two main areas: the Mexican Transition Zone and the Mexican Central Plateau. Ferns play an important role in the Mexican biodiversity and contributing to the beta diversity of Mexico.