干旱区生态环境知识资源中心

Our aim was to assess the conservation status of the cactus Ariocarpus scaphirostris by describing its population dynamics and spatial distribution in the only known large population left. Population dynamics were analyzed with the use of matrix projection models from a census period that encompassed 2 yr ( 2005 and 2006). Density of the individuals (0.25 individuals/m(2)) changed when compared with previous studies, and similar to other dense globose cacti, the pattern of spatial distribution was aggregated. Our results indicate that the original population has decreased considerably during a 20-yr period (r = -0: 08 individuals/individual/yr). However, on the basis of annual projections, the population is stable at equilibrium and could even show moderate growth ( l 1: 07 6 0: 17). When we simulated changes in survival, we found no significant decreases in l, basically because of the equal distribution of elasticities for survival. When growth was changed, l decreased by 10%. Ariocarpus scaphirostris needs to be revaluated because the demographic evaluation assigns a higher risk ( in risk of extinction) than that to which it is currently assigned ( vulnerable); the actual size of the population compared with historical data shows the species has reduced its population by more than 80% in 20 yr.