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Density-dependent selection in a fluctuating ungulate population

P R Moorcroft1, S D Albon, J M Pemberton

  • 1Department of Zoology, University of Cambridge, U.K.

Proceedings. Biological Sciences
|January 22, 1996
PubMed
Summary

Density-dependent natural selection impacts Soay sheep survival, with stronger selection at high population densities. This research provides direct evidence of selection influencing population dynamics in a natural setting.

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Area of Science:

  • Ecology
  • Evolutionary Biology
  • Population Genetics

Background:

  • Natural selection is a key evolutionary driver, but its direct link to population density and simple genetic variation in wild populations remains under-documented.
  • Polymorphisms, such as coat color and horn type, offer observable traits to study selective pressures.

Purpose of the Study:

  • To provide direct evidence of density-dependent natural selection acting on simple polymorphic traits in a natural population.
  • To investigate the relationship between population density and selective survival differences in Soay sheep.

Main Methods:

  • Field observations and survival data collection from Soay sheep (Ovis aries) on St Kilda, Scotland.
  • Analysis of selective differences in survival related to coat color and horn type polymorphisms across varying population densities.

Related Experiment Videos

  • Assessment of overcompensatory mortality in relation to genetic variation in morph traits.

    • Main Results:

    • Demonstrated density-dependent 'soft' selection on coat color and horn type in Soay sheep.
    • Selective survival differences were significantly stronger in high-density years and weaker in low-density years.
    • Overcompensatory mortality, linked to population instability, was higher when accounting for genetic variation in these traits.

    Conclusions:

    • This study provides the first direct evidence of density-dependent natural selection on simple polymorphisms in a natural population.
    • Understanding the interplay between selection and population demography is crucial for both ecological and genetic research.
    • Genetic variation in key traits can influence population dynamics and instability.