MODELLING THE REINTRODUCTION OF THE GREATER BILBY Macrotis lagotis USING THE METAPOPULATION MODEL ANALYSIS OF THE LIKELIHOOD OF EXTINCTION (ALEX)

Abstract Population viability analysis of the greater bilby Macrotis lagotis was conducted using the metapopulation model ALEX. ALEX was used to examine the effect of reintroduction configurations and potential manipulations on the extinction risk of the metapopulation. More specifically, the impact of patch separation, sporadic big rains and fire on population survival was investigated. Estimates of population parameters, including survival and fecundity, dispersal rate and home range size, were derived from a bilby reintroduction programme conducted in central Australia, as were parameters describing environmental quality and the impact of fire, drought and sporadic large rainfall events. The modelling results indicated that local segregation of a population to achieve replication did not change extinction risk dramatically and that an experiment for a 2-year duration (equivalent to a generation time) could be achieved at low risk with a small population. Adult mortality was of key importance in determining population survival. With the release of 12 individuals, drought and sporadic high rainfall events limited the life of the reintroduced population to a median of 8 years. In the absence of these events, median extinction time was extended to 26 years. The modelling indicated that there was little scope to reduce environmental variation (and improve the population survival prospects) through manipulation or management of the environment. However, spatially subdividing subpopulations so that they should experience appreciably different big rainfall and drought events has potential to reduce metapopulation extinction risk.