Black-footed ferret (Mustela nigripes) population dynamics : use of simulation modeling to investigate the effects of stochasticity, habitat geometry and dispersal

This study employed a computer simulation model to investigate the population dynamics of the black-footed ferret (Mustela nigripes). Three different black-footed ferret habitat sites were used in the study: the Meeteetse, Wyoming site, a site in Northern Montana, and a hypothetical complex. The model was fully stochastic and included details of BFF demography and life history, with particular attention given to the juvenile dispersal process. Actual prairie dog colony geography of each study site was approximated in the simulation by use of a hexagonal grid, and dispersal was modeled by moving individuals in discrete steps on the grid. We investigated the effects of demographic and environmental stochasticity, prairie dog colony distribution and dispersal success. Results supported seven conclusions: 1) demographic stochasticity has little effect on population persistence except when population size is extremely small; 2) increasing environmental stochasticity decreases population persistence substantially; 3) mean population size is much lower than the carrying capacity for the habitat; 4) extinction is more likely to occur when the number of occupied colonies becomes too low; 5) increase in dispersal mortality decreases population persistence; 6) the Meeteetse-tuned model may not accurately predict population trends on other sites without parameter changes; 7) introduction of small stepping stone colonies increases the frequency of successful colonizations from one large colony to another located some distance away. Secondary observations and management implications are also discussed.