Relative contributions of sampling error in initial population size and vital rates to outcomes of population viability analysis

We evaluated the relative contributions of sampling error (randomly chosen standard errors applied as 0-30% of parameter estimates) in initial population size and vital rates (survival and reproduction) to the outcome of a simulated population viability analysis for grizzly bears (Ursus arctos). Error in initial population size accounted for the largest source of variation (model II analysis of variance, F-25.5 = 10.8. p = 0.00001) in simulation outcomes, explaining 60.5% of the variance. In contrast, error in vital rates contributed little to simulation outcomes (F-25.5 = 0.61, p = 0.70). accounting for only 2.4% of model variation. Reduced global variation in vital rates, as a result of independent random sampling of annual deviates for each parameter, likely contributed to the results. Errors in estimates of initial population size, if ignored in PVA, have the potential to leave maanagers with estimates of population persistence that air of little value for making management decisions.