Biotic and abiotic factors related to the spatial distribution of the endangered cacti Ariocarpus kotschoubeyanus

Background/Question/Methods Ariocarpus kotschoubeyanus is a Mexican endemic species, officially classified as endangered since it is threatened by illegal extraction. We analyzed the nurse plant interactions to understand the recruitment, distribution and survival patterns of the populations. We used the SADIE system (Spatial analysis by Distance IndicEs) to analyze the spatial distribution of A. kotschoubeyanus and its positive (nursing) and negative interactions with the dominant shrub species. We studied also the principal microclimatic factors (light, temperature and surface moisture) and the soil microconditions in the study area.

Results/Conclusions . A. kotschoubeyanus have an aggregated distribution (Ia= 2.114) with patches in areas lacking vegetation cover. The dominant shrub species also have aggregated distributions. A. kotschoubeyanus was positively associated with two creeping plants Tiquilia sp (X=0.379, P<0.0001) and Opuntia meijmeri (X=0.2753, P P<0.0001), and was negatively associated with shrubs that exhibited high importance value (IV) and canopies that offered buffered environmental conditions such as Karwinskia humboldtiana (X=-0.1948, P<0.9803), Calanticaria bicolor (X=-0.2568, P<0.9982). The remaining shrub species showed the same negative association pattern with the cacti, which lead us to reject any nursing interaction with the vegetation. Apparently soil rocks are the main factor altering the local microclimate, facilitating the establishment of A. kotschoubeyanus.