Structural uncertainty in stochastic population models: delayed development in the eastern barred bandicoot, Perameles gunnii

Uncertainty about which model structure best describes the life history of a species may be a problem for the development of some population viability analysis (PVA). This paper describes the development and exploration of two structurally different stochastic population models when there is uncertainty about the life history of a species. Delayed reproduction was observed in a protected population of the small marsupial Perameles gunnii (eastern barred bandicoot) at Woodlands Historic Park, Victoria, Australia. This previously undocumented feature of P. gunnii may be considered to be either a component of the seasonal breeding cycle or it may be delayed development to sexual maturity. A delayed development model is compared to a standard development model where the parameter estimates of each model were obtained from a long-term mark-recapture study at Woodlands Historic Park. While the growth rate of the delayed development model is less than that of the standard model, the predicted risks of extinction/quasiextinction were higher for the standard model. This discrepancy is the result of different interpretations placed upon the available data underpinning the two models, the most important of which is the difference between the estimated variance in survivorship of the sub-adult stage. The results highlight the need for conservation assessments based on stochastic modelling to explore the degree to which the predicted extinction risk is affected by the incomplete knowledge of the species’ basic biology and parameter values.