Genetic estimates of contemporary effective population size: what can they tell us about the importance of genetic stochasticity for wild population persistence?
Article first published online: 28 JUN 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
Volume 17, Issue 15, pages 3428–3447, August 2008
How to Cite
PALSTRA, F. P. and RUZZANTE, D. E. (2008), Genetic estimates of contemporary effective population size: what can they tell us about the importance of genetic stochasticity for wild population persistence?. Molecular Ecology, 17: 3428–3447. doi: 10.1111/j.1365-294X.2008.03842.x
- Issue published online: 19 JUL 2008
- Article first published online: 28 JUN 2008
- Received 23 December 2007; revision received 18 April 2008; accepted 06 May 2008
- effective population size;
- gene flow;
- genetic stochasticity;
- genetic compensation;
- inbreeding depression;
- marine fish;
- metapopulation dynamics;
- model bias;
- population fragmentation;
- sample size;
- Salmo salar;
- temporal method
Genetic stochasticity due to small population size contributes to population extinction, especially when population fragmentation disrupts gene flow. Estimates of effective population size (Ne) can therefore be informative about population persistence, but there is a need for an assessment of their consistency and informative relevance. Here we review the body of empirical estimates of Ne for wild populations obtained with the temporal genetic method and published since Frankham's (1995) review. Theoretical considerations have identified important sources of bias for this analytical approach, and we use empirical data to investigate the extent of these biases. We find that particularly model selection and sampling require more attention in future studies.
We report a median unbiased Ne estimate of 260 (among 83 studies) and find that this median estimate tends to be smaller for populations of conservation concern, which may therefore be more sensitive to genetic stochasticity. Furthermore, we report a median Ne/N ratio of 0.14, and find that this ratio may actually be higher for small populations, suggesting changes in biological interactions at low population abundances. We confirm the role of gene flow in countering genetic stochasticity by finding that Ne correlates strongest with neutral genetic metrics when populations can be considered isolated. This underlines the importance of gene flow for the estimation of Ne, and of population connectivity for conservation in general. Reductions in contemporary gene flow due to ongoing habitat fragmentation will likely increase the prevalence of genetic stochasticity, which should therefore remain a focal point in the conservation of biodiversity.