PARENT SESSION
Oral Session #1: Conservation Ecology: Threatened and Endangered Species. Presiding: W. Bond.
Monday, August 6, 2001. 8:00 AM to 12:15 PM. Madison Ballroom C.
How precise is population viability analysis (PVA)?
Ellner, Stephen1, Fieberg, John2, Ludwig, Donald3, Wilcox, Chris4, 1 2 3 4
ABSTRACT- PVA is widely used in conservation biology to predict extinction risk for threatened species and to compare management options for species preservation. But according to some recent studies, PVA risk estimates based on typical data sets are so imprecise as to be meaningless. "Confidence intervals are so wide that the analysis provides little or no information about the magnitude of extinction probabilities" (Ludwig 1999, Ecology 80: 298-310). "The data requirements for estimates of extinction risk are overwhelming" (Fieberg and Ellner 2000, Ecology 81: 2040-2047). In contrast, Brook et al. (2000, Nature 404: 385-387) claim to have shown that PVA is "a valid and sufficiently accurate tool for categorizing and managing endangered species...these results provide strong empirical justification for the use of PVA for categorizing the vulnerability of endangered animal species and evaluating options for their recovery". We show that these differing conclusions result from the fact that the Brook et al. (2000) tests are sensitive to the bias of risk estimates, but not to the variability of species-by-species estimates. These two properties (low bias, high variance) suggest that PVA will be more useful for within-species than for between-species comparisons.
KEY WORDS: population viability analysis, risk assessment