ON THE USE OF DEMOGRAPHIC-MODELS OF POPULATION VIABILITY IN ENDANGERED SPECIES MANAGEMENT

We examine why demographic models should be used cautiously in Populat ion Viability Analysis (PVA) with endangered species. We review the st ructure, data requirements, and outputs of analytical, deterministic s ingle-population, stochastic single-population, metapopulation, and sp atially explicit models. We believe predictions from quantitative mode ls for endangered species are unreliable due to poor quality of demogr aphic data used in most: applications, difficulties in estimating vari ance in demographic rates, and lack of information on dispersal (dista nces, ages, mortality, movement patterns). Unreliable estimates also a rise because stochastic models are difficult to validate, environmenta l trends and periodic fluctuations are rarely considered, the form of density dependence is frequently unknown but greatly affects model out comes, and alternative model structures can result in very different p redicted effects of management regimes. We suggest that PVA (1) evalua te relative rather than absolute rates of extinction, (2) emphasize sh ort-time periods for making projections, (3) start with simple models and choose an approach that data can support, (4) use models cautiousl y to diagnose causes of decline and examine potential routes to recove ry (5) evaluate cumulative ending functions and alternative reference points rather than extinction rates, (6) examine all feasible scenario s, and (7) mix genetic and demographic currencies sparingly. Links bet ween recovery options and PVA models should be established by conducti ng; field tests of model assumptions and field validation of secondary model predictions.