Modeling effects of nonbreeders on population growth estimates

Aline M Lee, Jane M Reid, Steven R Beissinger

Research output: Contribution to journalArticle

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Abstract

1.Adult individuals that do not breed in a given year occur in a wide range of natural populations. However, such nonbreeders are often ignored in theoretical and empirical population studies, limiting our knowledge of how nonbreeders affect realized and estimated population dynamics and potentially impeding projection of deterministic and stochastic population growth rates. 2.We present and analyze a general modeling framework for systems where breeders and nonbreeders differ in key demographic rates, incorporating different forms of nonbreeding, different life histories, and frequency-dependent effects of nonbreeders on demographic rates of breeders. 3.Comparisons of estimates of deterministic population growth rate, λ, and demographic variance, σ(2) d , from models with and without distinct nonbreeder classes show that models that do not explicitly incorporate nonbreeders give upwardly biased estimates of σ(2) d , particularly when the equilibrium ratio of nonbreeders to breeders, N*nb/N*b, is high. Estimates of λ from empirical observations of breeders only are substantially inflated when individuals frequently re-enter the breeding population after periods of nonbreeding. 4.Sensitivity analyses of diverse parameterizations of our model framework, with and without negative frequency-dependent effects of nonbreeders on breeder demographic rates, show how changes in demographic rates of breeders versus nonbreeders differentially affect λ. In particular, λ is most sensitive to nonbreeder parameters in long-lived species, when N*nb/N*b > 0, and when individuals are unlikely to breed at several consecutive time steps. 5.Our results demonstrate that failing to account for nonbreeders in population studies can obscure low population growth rates that should cause management concern. Quantifying the size and demography of the nonbreeding section of populations and modeling appropriate demographic structuring is therefore essential to evaluate nonbreeders' influence on deterministic and stochastic population dynamics. This article is protected by copyright. All rights reserved.

Original languageEnglish
Pages (from-to)75-87
Number of pages14
JournalJournal of Animal Ecology
Volume86
Issue number1
Early online date13 Oct 2016
DOIs
Publication statusPublished - Jan 2017

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population growth
demographic statistics
modeling
population dynamics
breeding population
demography
breeds
parameterization
life history
effect
rate
breeding

Keywords

  • demographic stochasticity
  • floaters
  • intermittent breeding
  • matrix model
  • non-breeding
  • population dynamics
  • reproductive skipping
  • sensitivity analysis

Cite this

Modeling effects of nonbreeders on population growth estimates. / Lee, Aline M; Reid, Jane M; Beissinger, Steven R.

In: Journal of Animal Ecology, Vol. 86, No. 1, 01.2017, p. 75-87.

Research output: Contribution to journalArticle

Lee, Aline M ; Reid, Jane M ; Beissinger, Steven R. / Modeling effects of nonbreeders on population growth estimates. In: Journal of Animal Ecology. 2017 ; Vol. 86, No. 1. pp. 75-87.
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abstract = "1.Adult individuals that do not breed in a given year occur in a wide range of natural populations. However, such nonbreeders are often ignored in theoretical and empirical population studies, limiting our knowledge of how nonbreeders affect realized and estimated population dynamics and potentially impeding projection of deterministic and stochastic population growth rates. 2.We present and analyze a general modeling framework for systems where breeders and nonbreeders differ in key demographic rates, incorporating different forms of nonbreeding, different life histories, and frequency-dependent effects of nonbreeders on demographic rates of breeders. 3.Comparisons of estimates of deterministic population growth rate, λ, and demographic variance, σ(2) d , from models with and without distinct nonbreeder classes show that models that do not explicitly incorporate nonbreeders give upwardly biased estimates of σ(2) d , particularly when the equilibrium ratio of nonbreeders to breeders, N*nb/N*b, is high. Estimates of λ from empirical observations of breeders only are substantially inflated when individuals frequently re-enter the breeding population after periods of nonbreeding. 4.Sensitivity analyses of diverse parameterizations of our model framework, with and without negative frequency-dependent effects of nonbreeders on breeder demographic rates, show how changes in demographic rates of breeders versus nonbreeders differentially affect λ. In particular, λ is most sensitive to nonbreeder parameters in long-lived species, when N*nb/N*b > 0, and when individuals are unlikely to breed at several consecutive time steps. 5.Our results demonstrate that failing to account for nonbreeders in population studies can obscure low population growth rates that should cause management concern. Quantifying the size and demography of the nonbreeding section of populations and modeling appropriate demographic structuring is therefore essential to evaluate nonbreeders' influence on deterministic and stochastic population dynamics. This article is protected by copyright. All rights reserved.",
keywords = "demographic stochasticity, floaters, intermittent breeding, matrix model, non-breeding, population dynamics, reproductive skipping, sensitivity analysis",
author = "Lee, {Aline M} and Reid, {Jane M} and Beissinger, {Steven R}",
note = "Acknowledgements We thank the Beissinger lab and reviewers for helpful comments on manuscript drafts. This research was funded by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (project NON- BREEDERS). The contents of this paper reflect the views of the researchers, not the views of the European Commission. Data Accessibility R-code available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.t56cn (Lee, Reid & Beissinger, 2016).",
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N1 - Acknowledgements We thank the Beissinger lab and reviewers for helpful comments on manuscript drafts. This research was funded by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (project NON- BREEDERS). The contents of this paper reflect the views of the researchers, not the views of the European Commission. Data Accessibility R-code available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.t56cn (Lee, Reid & Beissinger, 2016).

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N2 - 1.Adult individuals that do not breed in a given year occur in a wide range of natural populations. However, such nonbreeders are often ignored in theoretical and empirical population studies, limiting our knowledge of how nonbreeders affect realized and estimated population dynamics and potentially impeding projection of deterministic and stochastic population growth rates. 2.We present and analyze a general modeling framework for systems where breeders and nonbreeders differ in key demographic rates, incorporating different forms of nonbreeding, different life histories, and frequency-dependent effects of nonbreeders on demographic rates of breeders. 3.Comparisons of estimates of deterministic population growth rate, λ, and demographic variance, σ(2) d , from models with and without distinct nonbreeder classes show that models that do not explicitly incorporate nonbreeders give upwardly biased estimates of σ(2) d , particularly when the equilibrium ratio of nonbreeders to breeders, N*nb/N*b, is high. Estimates of λ from empirical observations of breeders only are substantially inflated when individuals frequently re-enter the breeding population after periods of nonbreeding. 4.Sensitivity analyses of diverse parameterizations of our model framework, with and without negative frequency-dependent effects of nonbreeders on breeder demographic rates, show how changes in demographic rates of breeders versus nonbreeders differentially affect λ. In particular, λ is most sensitive to nonbreeder parameters in long-lived species, when N*nb/N*b > 0, and when individuals are unlikely to breed at several consecutive time steps. 5.Our results demonstrate that failing to account for nonbreeders in population studies can obscure low population growth rates that should cause management concern. Quantifying the size and demography of the nonbreeding section of populations and modeling appropriate demographic structuring is therefore essential to evaluate nonbreeders' influence on deterministic and stochastic population dynamics. This article is protected by copyright. All rights reserved.

AB - 1.Adult individuals that do not breed in a given year occur in a wide range of natural populations. However, such nonbreeders are often ignored in theoretical and empirical population studies, limiting our knowledge of how nonbreeders affect realized and estimated population dynamics and potentially impeding projection of deterministic and stochastic population growth rates. 2.We present and analyze a general modeling framework for systems where breeders and nonbreeders differ in key demographic rates, incorporating different forms of nonbreeding, different life histories, and frequency-dependent effects of nonbreeders on demographic rates of breeders. 3.Comparisons of estimates of deterministic population growth rate, λ, and demographic variance, σ(2) d , from models with and without distinct nonbreeder classes show that models that do not explicitly incorporate nonbreeders give upwardly biased estimates of σ(2) d , particularly when the equilibrium ratio of nonbreeders to breeders, N*nb/N*b, is high. Estimates of λ from empirical observations of breeders only are substantially inflated when individuals frequently re-enter the breeding population after periods of nonbreeding. 4.Sensitivity analyses of diverse parameterizations of our model framework, with and without negative frequency-dependent effects of nonbreeders on breeder demographic rates, show how changes in demographic rates of breeders versus nonbreeders differentially affect λ. In particular, λ is most sensitive to nonbreeder parameters in long-lived species, when N*nb/N*b > 0, and when individuals are unlikely to breed at several consecutive time steps. 5.Our results demonstrate that failing to account for nonbreeders in population studies can obscure low population growth rates that should cause management concern. Quantifying the size and demography of the nonbreeding section of populations and modeling appropriate demographic structuring is therefore essential to evaluate nonbreeders' influence on deterministic and stochastic population dynamics. This article is protected by copyright. All rights reserved.

KW - demographic stochasticity

KW - floaters

KW - intermittent breeding

KW - matrix model

KW - non-breeding

KW - population dynamics

KW - reproductive skipping

KW - sensitivity analysis

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JO - Journal of Animal Ecology

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