SPATIAL DISTRIBUTION AND ASSOCIATION WITH NURSE PLANTS OF THE BISHOP'S MITER CACTUS ASTROPHYTUM MYRIOSTIGMA IN THE CHIHUAHUAN DESERT

Abstract

Nurse-protege interactions facilitate seedling establishment of many cacti species and might promote spatial aggregation of plants. In June 2014, we analyzed the spatial distribution pattern with Ripley's K-function and the possible association of Astrophytum myriostigma with nurse plants in two populations (Rioverde and Pozas, San Luis Potosi, Mexico). We estimated canopy cover of perennial plant species with a logarithmic scale method and determined the association, size, and orientation of A. myriostigma in relation to nurse plants. Astrophytum myriostigma had an aggregated distribution pattern; approximately 50% were associated with nurse plants at Rioverde and 63% at Pozas, with Hechtia glomerata (Bromeliaceae) being the main nurse plant species in both populations. Cacti associated with nurse plants at Pozas were larger than those not associated, and they did not have any significant orientation in relation to the nurse plant crown. In contrast, the size of associated and nonassociated cacti at Rioverde was similar, but they were established significantly more frequently under the north side of the nurse plant. The association of A. myriostigma with nurse plants is facultative, through either nurse plant protection or open spaces, likely related with abiotic nurses. Understanding nurse plant associations will help target key species for conservation and identify the most likely associations to increase the survival of reintroduced individuals.