Reliability of Absolute and Relative Predictions of Population Persistence Based on Time Series

• Published in: Conservation biology Vol. 18; no. 5; pp. 1224 - 1232
• Main Authors: LOTTS, KELLY C., WAITE, THOMAS A., VUCETICH, JOHN A.
• Format: Journal Article
• Language: English
• Published: 350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK Blackwell Publishing Inc 01.10.2004; Blackwell Science; Blackwell
• Subjects: Animal, plant and microbial ecology; análisis de viabilidad poblacional; Applied ecology; aproximación difusión; Autocorrelation; Biological and medical sciences; Conservation biology; Conservation, protection and management of environment and wildlife; diffusion approximation; endangered species; especies en peligro; evaluación de riesgo; extinción; extinction; Fundamental and applied biological sciences. Psychology; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; Population estimates; Population growth rate; population viability analysis; Risk analysis; risk assessment; series de tiempo; Species extinction; Statistical variance; Time series; Time series forecasting; Viability; Persistence; Reliability; Environmental protection
• ISSN: 0888-8892; 1523-1739
• DOI: 10.1111/j.1523-1739.2004.00285.x

Conventional population viability analysis (PVA) is often impractical because data are scarce for many threatened species. For this reason, simple count-based models are being advocated. The simplest of these models requires nothing more than a time series of abundance estimates, from which variance and autocorrelation in growth rate are estimated and predictions of population persistence are generated. What remains unclear, however, is how many years of data are needed to generate reliable estimates of these parameters and hence reliable predictions of persistence. By analyzing published and simulated time series, we show that several decades of data are needed. Predictions based on short time series were very unreliable mainly because limited data yielded biased, unreliable estimates of variance in growth rate, especially when growth rate was strongly autocorrelated. More optimistically, our results suggest that count-based PVA is sometimes useful for relative risk assessment (i.e., for ranking populations by extinction risk), even when time series are only a decade long. However, some conditions consistently lead to backward rankings. We explored the limited conditions under which simple count-based PVA may be useful for relative risk assessment.