. Preservation of endangered plants depends on the knowledge of ecological data, such as the population structure, their spatial distribution, and the identification of the most vulnerable stages of its life cycle. Cactus species are threatened due to their ornamental value, long life cycles, specific habitat, and transformation of their habitat by human causes. In this work, we describe the population structure and the pattern of spatial distribution of the globose cactus Coryphantha elephantidens
, a species protected by the Mexican law. The study was conducted in a site of tropical dry forest of Sierra de Huautla, central Mexico, characterized by chronic disturbance due to livestock grazing and wood extraction. On summer 2015, we selected ten patches of open vegetation, where this cactus grow. For each plant (n =
201 plants), we recorded stem number, tubercle number, diameter of the stem, and flower number. Population was divided into five categories according to size and stage of life cycle: seedling, juveniles, and three categories of adults. We mapped all individual plants by means of a distance-based sampling for further location and for obtaining the Hopkins index, which indicates the pattern of spatial distribution. On 2016, we included more individuals to obtain the population structure, and compared population structure with that of 2015.
Results indicated that adults (92%) dominated the population in 2015, and only 7% and 1% of individuals were juveniles and seedlings, respectively (n = 201 plants). In 2016, population structure changed: both seedlings and juveniles were 15% of individuals each, and adults represented 60% of population (n = 400 plants). Population density in 2015 was 1 plant/50m2, which is low compared with other globose cacti. Hopkins index was 0.75, indicating that spatial distribution pattern is aggregated. The aggregated pattern of spatial distribution could be related to environmental conditions in the open vegetation: in these sites, individuals of C. elephantidens receive enough light to grow without competing with other plants. In this sense, open sites that follow disturbance could favor cactus grow, compared with the primary vegetation characteristic of the tropical dry forest. The population structure dominated by adults (2015) indicates low recruitment in the population; however, the change observed during 2016 indicates that recruitment pulses can occur, probably related to environmental factors, or that recruitment is highly heterogeneous across space.