Conservation of rare species involves knowing where they are found and how many individuals are in a population. If a species can only survive in certain habitats, then any changes to that habitat can drive a species to extinction. Similarly, as the population size decreases, chance events can have an increasing impact. </p> A rare cactus found only in western Colorado has recently been recommended for delisting from the Endangered Species Act because we know more about its natural history now than we did at the time of listing. We have a clearer understanding of how much genetic diversity is present within and among populations (enough to propose naming a new species). We know more about how survival, growth and reproductive rates drive population size (pretty stable). Lastly, and maybe most importantly to this decision, we have better estimates of the number of individuals in each population (many more than previously documented). Estimates of the minimum cactus abundance provide a snapshot of the current status and show that population sizes are large enough to persist through random fluctuations in germination and reproduction. </p>
