Assessing human impact despite uncertainty: viability of the northern spotted owl metapopulation in the northwestern USA

We demonstrate the effect of uncertainty (resulting from lack of informatio n or measurement error) on the assessment of human impact, with an analysis of the viability of the northern spotted owl throughout its range in the U nited States. We developed a spatially-explicit, stage-structured, stochast ic metapopulation model of the northern spotted owl throughout its range in the United States. We evaluated the viability of the metapopulation using measures such as risk of decline and time to extinction. We incorporated un certainty in the form of parameter ranges, and used them to estimate upper and lower bounds on the estimated viability of the species. We analysed the effect of this type of uncertainty on the assessment of human impact by co mparing the species' viability under current conditions and under an assume d loss of spotted owl habitat in the next 100 years. The ranges of paramete rs were quite large and resulted in a wide range of risks of extinction. De spite this uncertainty, the results were sensitive to parameters related to habitat loss: under all assumptions and combinations of parameters, the mo del predicted that habitat loss results in substantially higher risks of me tapopulation decline. This result demonstrated that even with relatively la rge uncertainties, risk-based model results can be used to assess human imp act reliably.