Cuatro Ciénegas as a Refuge for the Living Rock Cactus, Ariocarpus fissuratus: Demographic and Conservation Studies

Ariocarpus fissuratus is a subglobose cactus, endemic of the Chihuahuan Desert, from San Luis Potosi, Mexico to south of Texas, restricted to limestone soils. Its stem resembles the soil surface where it grows; therefore, it is commonly known as “living rock” or falso peyote. Under harsh conditions, its taproot shrinks, enhancing its survival by making the plant less visible to predators and reducing its exposure to high temperature and water loss. Due to its intriguing morphology and the beauty of their flowers it is highly appreciated by illegal collectors, that along with recent habitat loss have driven the species near extinction. We studied the population ecology with data obtained during the years 2005–2009 of the species in three populations with contrasting densities and distribution of size classes in the Cuatro Cienegas Basin. We found that the populations are stable (neither increasing nor decreasing in numbers) and Cuatro Cienegas Basin contains the largest populations of A. fissuratus along its distribution. Moreover, the populations have variable densities, and differences in plant sizes, individual growth rates and survival probabilities, flowering, fruit and seed production, and pollinator behavior. Individual reproductive success, estimated as fruit and seed production, decreases at low population densities, in comparison to reproductive success of individuals located at high population densities, suggesting that a large population size is required to ensure efficient pollination. Overall, Cuatro Cienegas Basin is the most important area for this living rock conservation, because it offers protection to the populations and its interacting species, especially its pollinators, which are solitary bees.