Prediction of the minimum effective size of a population viable in the long term

Abstract The establishment of the minimum size for a viable population (MVP) has been used as a guidance in conservation practice to determine the extinction risks of populations and species. A consensus MVP rule of 50/500 individuals has been attained, according to which a minimum effective population size of N e = 50 is needed to avoid extinction due to inbreeding depression in the short term, and of N e = 500 to survive in the long term. However, the large inbreeding loads ( B ) usually found in nature, as well as the consideration of selection affecting genetic diversity, have led to suggest that those numbers should be doubled (100/1000). However, none of these modified rules have considered the consequences of purging of deleterious mutations. In a previous simulation study, the reduction of B by the action of purging pointed towards a MVP intermediate between the two previous rules for short term survival. Here, we focused on the consequences of purging in the establishment of MVPs for long term survival. We performed computer simulations of populations under the action of purging, drift, new mutation, and environmental effects on fitness to investigate the extinction times and the loss of genetic diversity. Our results indicate that purging can reduce the MVP needed for a population to persist in the long term, with estimates close to N e = 500 for species with moderately large reproductive rates. However, MVP values appear to be of at least N e = 1000 when the species´ reproductive rates are low.