Effects of population characteristics and structure on estimates of effective population size in a house sparrow metapopulation

Authors

  • Helle Tessand Baalsrud,

    1. Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Current affiliation:
    1. Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, Oslo, Norway
    Search for more papers by this author
  • Bernt-Erik Sæther,

    1. Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Search for more papers by this author
  • Ingerid Julie Hagen,

    1. Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Search for more papers by this author
  • Ane Marlene Myhre,

    1. Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Search for more papers by this author
  • Thor Harald Ringsby,

    1. Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Search for more papers by this author
  • Henrik Pärn,

    1. Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Search for more papers by this author
  • Henrik Jensen

    Corresponding author
    1. Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Search for more papers by this author

Abstract

Effective population size (Ne) is a key parameter to understand evolutionary processes and the viability of endangered populations as it determines the rate of genetic drift and inbreeding. Low Ne can lead to inbreeding depression and reduced population adaptability. In this study, we estimated contemporary Ne using genetic estimators (LDNE, ONeSAMP, MLNE and CoNe) as well as a demographic estimator in a natural insular house sparrow metapopulation. We investigated whether population characteristics (population size, sex ratio, immigration rate, variance in population size and population growth rate) explained variation within and among populations in the ratio of effective to census population size (Ne/Nc). In general, Ne/Nc ratios increased with immigration rates. Genetic Ne was much larger than demographic Ne, probably due to a greater effect of immigration on genetic than demographic processes in local populations. Moreover, although estimates of genetic Ne seemed to track Nc quite well, the genetic Ne-estimates were often larger than Nc within populations. Estimates of genetic Ne for the metapopulation were however within the expected range (<Nc). Our results suggest that in fragmented populations, even low levels of gene flow may have important consequences for the interpretation of genetic estimates of Ne. Consequently, further studies are needed to understand how Ne estimated in local populations or the total metapopulation relates to actual rates of genetic drift and inbreeding.

Ancillary