The impact of inbreeding depression on population survival depending on demographic parameters

Inbreeding depression is a critical phenomenon for conservation of small populations, especially concerning the captive breeding of endangered animals whose effective population size may be very low. In order to manage such captive populations on a long-term basis, assessment of the interactions between demographic and genetic parameters and their consequences on the population survival probability is essential. Therefore, we examined (1) the relative importance of initial population size and carrying capacity on the survival probability of a population, (2) the impact of a bottleneck in an already inbred population. For this purpose, a stochastic model taking into account the effect of genes responsible for inbreeding depression was built. It was concluded that the population survival probability is very sensitive to the carrying capacity. Moreover, in inbred populations, a large increase in the extinction rate results from a second bottleneck. With two founders, survival is high as long as the carrying capacity is not very small (above a few decades), whereas a second bottleneck has a dramatic effect, even when the carrying capacity approaches 100. Consequently, previous inbreeding should be considered in the case of reintroduction. Reason for reintroduction failure could be successive bottlenecks, with the associated deleterious effects of inbreeding.