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

AE Trask, EM Bignal, DI McCracken, SB Piertney, JM Reid

Research output: Contribution to journalArticle

9 Citations (Scopus)
9 Downloads (Pure)

Abstract

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 (math formula) of 0.71. Females and males made similar overall contributions to math formula. 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.
Original languageEnglish
Pages (from-to)1082 - 1093
Number of pages12
JournalJournal of Animal Ecology
Volume86
Issue number5
Early online date3 Jul 2017
DOIs
Publication statusFirst published - 3 Jul 2017

Fingerprint

effective population size
stochasticity
wild population
viability
inbreeding
age class
immigration
demographic method
demography
disequilibrium
age structure
genetic variation
connectivity
population size
census
trajectory
gene
method
loss
rate

Bibliographical note

1030760
1031380
2064677

Keywords

  • Conservation genetics
  • Evolutionary potential
  • Iteroparity
  • Life-history variation
  • Population connectivity
  • Population management
  • Reproductive skew

Cite this

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title = "Estimating demographic contributions to effective population size in an age-structured wild population experiencing environmental and demographic stochasticity",
abstract = "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 (math formula) of 0.71. Females and males made similar overall contributions to math formula. 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.",
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Estimating demographic contributions to effective population size in an age-structured wild population experiencing environmental and demographic stochasticity. / Trask, AE; Bignal, EM; McCracken, DI; Piertney, SB; Reid, JM.

In: Journal of Animal Ecology, Vol. 86, No. 5, 03.07.2017, p. 1082 - 1093.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Estimating demographic contributions to effective population size in an age-structured wild population experiencing environmental and demographic stochasticity

AU - Trask, AE

AU - Bignal, EM

AU - McCracken, DI

AU - Piertney, SB

AU - Reid, JM

N1 - 1030760 1031380 2064677

PY - 2017/7/3

Y1 - 2017/7/3

N2 - 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 (math formula) of 0.71. Females and males made similar overall contributions to math formula. 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.

AB - 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 (math formula) of 0.71. Females and males made similar overall contributions to math formula. 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.

KW - Conservation genetics

KW - Evolutionary potential

KW - Iteroparity

KW - Life-history variation

KW - Population connectivity

KW - Population management

KW - Reproductive skew

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DO - 10.1111/1365-2656.12703

M3 - Article

VL - 86

SP - 1082

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JO - Journal of Animal Ecology

JF - Journal of Animal Ecology

SN - 0021-8790

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ER -