Preliminary Review : Current Range of the Threatened Bunched Cory Cactus in Defining Potential Habitat

The Bunched Cory Cactus (Cactaceae; Coryphantha ramillosa ssp. ramillosa) is a threatened species limited in the U.S. to the lower canyons of the Rio Grande in Brewster and Terrell Counties. Minimal information is known about the species range below the county level. To determine the likelihood of continued survival, with respect to the degrading influence of known threats to genetic diversity and population viability, available suitable habitat must be identified. To do so, surveys were conducted at known populations during the summer of 2014 to the spring 2015 in Big Bend National Park and on private lands. The main objective was to develop a potential habitat map based on observed abiotic attributes: elevation, slope, aspect, and rock formation. The habitat map was used to guide surveys in locating novel populations. The current map will be improved as observations from new sites are added. Currently, the potential habitat map suggests: if populations surveyed are representative of the typical preferred habitat, the species should not be widely-scattered. Based on the assumption of equal likelihood of colonization, the species is not limited by availability of suitable habitat. Some aspect of the species reproduction biology may be the limiting factor for occurrence. Future research plans include evaluating the map’s predictive accuracy and determining relative predictive power of abiotic variables through a weighted site selection or fuzzy logic approach. The final map will also be used for selection of sample populations for studies of the species’ reproductive biology and pollination ecology.