Restricted geographical distribution of Cremnophila Nutans (Crassulaceae): implications to the conservation of a micro-endemic, habitat specialist and ornamental Mexican plant

Abstract

Information on the extent of the geographic distribution and on the factors affecting the species geographic range is a valuable tool to identify conservation priorities and to protect biodiversity. We focused on Cremnophila nutans (Crassulaceae), a habitat specialist, micro-endemic and ornamental species distributed only in northern areas of the state of Morelos (municipality of Tepoztlan) in central Mexico. Following the criterions established by the International Union for Conservation of Nature, we estimated the range extent (34.9 km²) and area of occupancy (36 km²) of C. nutans. Based on our estimations C. nutans can be considered as a critically endangered species. From an extensive area of accessibility determined by combinations of climate and physiographic layers, the ecological niche modeling (22 occurrence records and three bioclimatic variables) predicted a restricted and stretch band of high habitat suitability coinciding majorly with northern areas of the state of Morelos. Habitat suitability was explained by annual mean temperature (72.5 %) and annual precipitation (25.3%). Potential areas with climatically suitable habitats could be in fact smaller because rocky outcrops usually colonized by C. nutans are not present along the entire potential area. Besides its restricted geographic distribution, C. nutans face threats derived from frequent forest fires, climate change, and extraction from its natural habitat. Management strategies strongly based on ex situ propagation and social working with local people are proposed to assure persistence of this unique rare plant species.