Title

Demographic Stochasticity and the Variance Reduction Effect

Document Type

Article

Publication Date

7-2002

Keywords

conservation biology, demography, extinction risk, homogeneous populations, pop ulation viability analysis, stochastic demography, variance reduction effect

Digital Object Identifier (DOI)

https://doi.org/10.2307/3071775

Abstract

Demographic stochasticity is almost universally modeled as sampling var iance in a homogeneous population, although it is defined as arising from random variation among individuals. This can lead to serious misestimation of the extinction risk in small populations. Here, we derive analytical expressions showing that the misestimation for each demographic parameter is exactly (in the case of survival) or approximately (in the case of fecundity) proportional to the among-individual variance in that parameter. We also show why this misestimation depends on systematic variation among individuals, rather than random variation. These results indicate that correctly assessing the importance of demo graphic stochasticity requires (1) an estimate of the variance in each demographic parameter; (2) information on the qualitative shape (convex or concave) of the mean-variance rela tionship; and (3) information on the mechanisms generating among-individual variation. An important consequence is that almost all population viability analyses (PVAs) over estimate the importance of demographic stochasticity and, therefore, the risk of extinction.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Ecology, v. 83, issue 7, p. 1928-1934

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