Endangered cacti in the chihuahuan desert .2. Biogeography and conservation

The distributions of the majority of the endangered cacti in the Chihuahuan Desert Region are concentrated in the southeastern and eastern segments of the area, where the predominance of narrow endemism is a remarkable phytogeographic phenomenon. We used three criteria-species richness, conservation value, and complementarity-to evaluate 37 cactus-rich area units in the Chihuahuan Desert. The evaluation of these three quantitative parameters together allowed us to determine that seven of these area (Huizache, Toliman, Ciudad Victoria, Metztitlan, Cuatro Cienegas, Jaumave, and Xichu) should be considered conservation priorities because they hold the most significant of endangered species, in terms of their numbers and their rarity. Conservation actions in these seven areas would protect 52 (55.9%) of the 93 endangered species studied here, most of which have extremely narrow distributions. Geographically, these critical areas are located in the Queretaroan-Hidalgoan arid zone (in the States of Queretaro, Hidalgo, and Guanajuato), in the Jaumave Valley (Tamaulipas), and in two disjunct areas (San Luis Potosi and Coahuila) in the interior of the Chihualuan Desert.