The effect of the initial age-class distribution on extinction risks: implications for the reintroduction of Leadbeater's possum

The success of a release programme may depend on the behaviour of individuals at small population sizes, on the number of individuals available for release, and on the demographic attributes of those individuals. If the initial age-class distribution is unlike the stable distribution, cycles of abundance may result, even in the absence of density dependence. Any cycle in total population abundance will bring a population regularly closer to extinction, resulting in elevated risks. The size and demography of the initial population could have an impact on risks through social dysfunction, and these factors may interact. An example is provided by Gymnobelideus leadbeateri. The authors investigate the effect of the initial population distribution and the number of animals released on extinction probabilities, using stage-based stochastic models. Results suggest that adults are more valuable in terms of reduction in risk than are subadults, and Allee effects may have important consequences for release strategies. -from Authors