Facilitation and its effect on vital rates of the living rock cactus Ariocarpus retusus

Abstract

Nurse plants modify environments conditions under their canopies, facilitating recruitment and benefiting protected plant. This effect varies with the life cycle stages and characteristics of interacting plants. We conducted a demographic study to understand the impacts of nurse plants on the vital rates of Ariocarpus retusus (Cactaceae) during two years. We identified the location of the cacti (open space, biotic nurse or abiotic nurse) and calculated their relative growth rates (RGRs). The population is numerically stable, with a tendency for growth in both years of study (λ = 1.008 and λ = 1.044). The highest sensitivity was in stasis, and the greatest vulnerability was in the seed to seedling transition. The RGR depends more on life stage than on microhabitat, it is high in seedlings and juveniles but drops below zero in adults. The association with biotic nurses is rare but reduces mortality and favors stasis. Fouquieria splendens, Hechtia sanchezii and Jatropha dioica supports many established cacti under its canopy, although they are not dominant species. Nurse plants' effects on fecundity vary and there is high fecundity in cacti associated with Turnera diffusa. Leaf phenology of this species may determine soil nutrient availability through leaf litter, providing resources for reproduction.