Estimating demographic contributions to effective population size in an age-structured wild population experiencing environmental and demographic stochasticity

Amanda E. Trask* (Corresponding Author), Eric M. Bignal, Davy I. McCracken, Stuart B. Piertney, Jane M. Reid

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)
18 Downloads (Pure)


1.A population's effective size (Ne ) is a key parameter that shapes rates of inbreeding and loss of genetic diversity, thereby influencing evolutionary processes and population viability. However estimating Ne , and identifying key demographic mechanisms that underlie the Ne to census population size (N) ratio, remains challenging, especially for small populations with overlapping generations and substantial environmental and demographic stochasticity and hence dynamic age-structure. 2.A sophisticated demographic method of estimating Ne /N, which uses Fisher's reproductive value to account for dynamic age-structure, has been formulated. However this method requires detailed individual- and population-level data on sex- and age-specific reproduction and survival, and has rarely been implemented. 3.Here we use the reproductive value method and detailed demographic data to estimate Ne /N for a small and apparently isolated red-billed chough (Pyrrhocorax pyrrhocorax) population of high conservation concern. We additionally calculated two single-sample molecular genetic estimates of Ne to corroborate the demographic estimate and examine evidence for unobserved immigration and gene flow. 4.The demographic estimate of Ne /N was 0.21, reflecting a high total demographic variance (σ(2)dg ) of 0.71. Females and males made similar overall contributions to σ(2)dg . However, contributions varied among sex-age classes, with greater contributions from 3 year-old females than males, but greater contributions from ≥5 year-old males than females. 5.The demographic estimate of Ne was ~30, suggesting that rates of increase of inbreeding and loss of genetic variation per generation will be relatively high. Molecular genetic estimates of Ne computed from linkage disequilibrium and approximate Bayesian computation were approximately 50 and 30 respectively, providing no evidence of substantial unobserved immigration which could bias demographic estimates of Ne . 6. Our analyses identify key sex-age classes contributing to demographic variance and thus decreasing Ne /N in a small age-structured population inhabiting a variable environment. They thereby demonstrate how assessments of Ne can incorporate stochastic sex- and age-specific demography and elucidate key demographic processes affecting a population's evolutionary trajectory and viability. Furthermore, our analyses show that Ne for the focal chough population is critically small, implying that management to re-establish genetic connectivity may be required to ensure population viability. This article is protected by copyright. All rights reserved.
Original languageEnglish
Pages (from-to)1082-1093
Number of pages12
JournalJournal of Animal Ecology
Issue number5
Early online date3 Jul 2017
Publication statusPublished - Sept 2017

Bibliographical note

We thank everyone who helped with fieldwork on Islay, in particular Sue Bignal and Pat Monaghan, as well as all land-owners and farmers who allowed access to nest sites. We thank Bernt-Erik Sӕther, Steinar Engen and Henrik Jensen for their generous help and discussions. AET was funded by the Natural Environment Research Council and Scottish Natural Heritage. JMR was supported by the European Research Council.


  • conservation genetics
  • evolutionary potential
  • iteroparity
  • life-history variation
  • population connectivity
  • population management
  • reproductive skew


Dive into the research topics of 'Estimating demographic contributions to effective population size in an age-structured wild population experiencing environmental and demographic stochasticity'. Together they form a unique fingerprint.

Cite this