Effects of Habitat Loss on the Ecology of Pachyphytum caesium (Crassulaceae), a Specialized Cliff-Dwelling Endemic Species in Central Mexico

Cliff-dwelling plant species are highly specialized and adapted to a vulnerable, fragmented, and are mostly endemic, narrowly-distributed and threatened. As a contribution to the conservation efforts of endemic cliff-dwelling species, this study provides an overview of the effects of habitat loss on the abundance and distribution of Pachyphytum caesium (Crassulaceae) due to human disturbances. To achieve this objective, we first conducted a retrospective analysis from 2003–2013 to assess the effects of land use change on the abundance of P. caesium. Secondly, we estimate the abundance and distribution of P. caesium throughout the study area, as well as analyze the effect of rock-climbing activities on the density and population structure of P. caesium. The results suggest differences in population abundance among sites is due to the adverse effects of habitat loss. P. caesium presents a very restricted distribution with small and fragmented populations. In addition, guava agriculture has a significant impact on the chemical soil properties of the hillsides, causing a significant effect on the occurrence of P. caesium, while sport activities remove both the soil and the plants from the cliffs. According to the results, P. caesium is classified as a plant species with extremely small populations (PSESP), and it is highly vulnerable to habitat disturbance. Its conservation is thus a priority to ensure its permanence.