Niche characteristics and potential distribution of Thelocactus species, a Mexican genus of globular cacti.

Aim: Although Mexican Cactaceae are a significative component of Mexican flora and have a relevant economic and ornamental value, the knowledge of the environmental factors characterising their niche is still quite incomplete. This study was aimed at defining the potential distribution and ecological niche of Thelocactus species. Methods: Climatic and environmental variables constraining the distribution of Thelocactus species were identified by means of environmental niche models (ENM) and ordination techniques, and used to generate potential distribution maps. The constructed ENMs were compared to assess the similarities of the ecological niche of Thelocactus species and to know if they share the same ecological niche space. Results: The distribution of Thelocactus species was mostly limited by a combination of two environmental factors, isothermality and precipitation of wettest quarter. The null hypothesis of the niche equivalency test was rejected for all paired comparisons between all Thelocactus species except between the pair Thelocactus leucacanthus-Thelocactus hastifer . The results of the niche similarity tests were quite varied, for some species pairs the niche similarities were higher than expected by chance, for others the null hypothesis was rejected, while in other species pairs niches were more similar than expected by chance, but only in one direction. Main conclusions: The differences in habitat requirements were well documented by the significative differences in the niche ecological space as shown by the equivalency test, while the high percentage of niches that were more similar than expected by chance suggest a high degree of niche conservatism among Thelocactus species. The spatial predictions could serve to improve field design sampling to discover new populations, while niche characteristics could be relevant for improving preservation actions and guiding reintroduction programs for a better conservation of Thelocactus species.