IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Ellner, S.P.; Fieberg, J.; Ludwig, D.; Wilcox, C. | |
| Precision of population viability analysis | |
| 2002 Conservation Biology (16): 258-261 | |
Although population viability analysis (PVA) is widely used in setting conservation policy, there is disagreement about the usefulness of this method. Objections have been raised concerning the precision of predictions in view of the short time series of data available and the sensitivity of estimates of extinction risk to estimated parameters (Hamilton & Moller 1995; Taylor 1995; Groom & Pascual 1998; Ludwig 1999). Beissinger and Westphal (1998) reviewed the use of demographic models for endangered-species management. They pointed out that poor data cause difficulties in parameter estimation. Which in turn lead to unreliable estimates of extinction risk. There are additional problems with model validation, especially if all available data have been used to estimate parameters. Beissinger and Westphal (1998) recommend that PVA be used to evaluate relative rather than absolute extinction risk, that projections be made only over short time periods, and that simple models be used rather than complicated ones. Fieberg and Ellner (2000) showed that values of the quasi-extinction probability - the probability of a decline to a lower population threshold - for a simple model range between 80% and 5% as the value of the intrinsic growth rate r varies between - 0.03 and +0.02. Such a range in estimates of r is common for data sets of moderate size. 'They also show that a precise estimate of extinction probability over a horizon of t years requires between 5t and 10t years of data, and that similar results hold for age-structured models. In a recent article, Brook et al. (2000) used field data on declining species to test the accuracy and bias of PVA models for predicting extinction risk and concluded that "PVA is a valid and sufficiently accurate tool for categorizing and managing endangered species." |
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