Short- and long-term population response to changes in vital rates: implications for population viability analysis
Conservation practitioners use demographic population viability analysis (PVA) to understand long-term effects of changing demographic rates on population growth rate. Sensitivities and elasticities of stage-specific survival and fertility rates provide managers with guidelines on the relative contributions of various life-history stages to long-term population growth. However, short-term patterns, especially single-year effects, of elasticity may be dramatically different from long-term effects, calling for caution in implementing management policies focusing entirely on only long- or short-term elasticities. Here we illustrate the temporal and spatial variation in elasticity patterns for four populations of California sea lions. Short-term stochastic elasticities were significantly different from long-term elasticities, and spatial patterns of short- and long-term elasticities varied across sites. These differences may be explained by transient effects in age structure and deviations from the stable age distribution, as well as environmental variation. Our results suggest that conservation practitioners should consider calculations of both short-and long-term elasticity in viability analyses that are used to guide management and should use caution in generalizing elasticity patterns across populations.