Hierarchical variation in phenotypic flexibility across timescales and associated survival selection shape the dynamics of partial seasonal migration

Paul Acker* (Corresponding Author), Francis Daunt, S. Wanless, Sarah J. Burthe, Mark Newell, M. P. Harris, Carrie Gunn, Robert Swann, Ana Payo-Payo, Jane Reid

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)
6 Downloads (Pure)


Population responses to environmental variation ultimately depend on within- individual and among-individual variation in labile phenotypic traits that affect fitness, and resulting episodes of selection. Yet, complex patterns of individual phenotypic variation arising within and between time periods, and associated variation in selection, have not been fully conceptualised or quantified. We highlight how structured patterns of phenotypic variation in dichotomous threshold traits can theoretically arise and experience varying forms of selection, shaping overall phenotypic dynamics. We then fit novel multistate models to ten years of band-resighting data from European shags to quantify phenotypic variation and selection in a key threshold trait underlying spatio- seasonal population dynamics: seasonal migration versus residence. First, we demonstrate substantial among-individual variation alongside substantial between-year individual repeatability in within-year phenotypic variation (‘flexibility’), with weak sexual dimorphism. Second, we demonstrate that between-year individual variation in within-year phenotypes (‘supraflexibility’) is structured and directional, consistent with the threshold trait model. Third, we demonstrate strong survival selection on within- year phenotypes, and hence on flexibility, that varies across years and sexes, including episodes of disruptive selection representing costs of flexibility. By quantitatively combining these results, we show how supraflexibility and survival selection on migratory flexibility jointly shape population-wide phenotypic dynamics of seasonal movement.
Original languageEnglish
Pages (from-to)269-286
Number of pages18
JournalThe American Naturalist
Issue number2
Early online date20 Dec 2022
Publication statusPublished - 1 Feb 2023

Bibliographical note

We thank everyone from UK Centre for Ecology & Hydrology and University of Aberdeen (UoA) who contributed to data collection, particularly Hannah Grist and Jenny Sturgeon; NatureScot for access to the Isle of May National Nature Reserve; Scottish Ornithologists' Club (SOC) for their support; and all volunteer observers, particularly Raymond Duncan and Moray Souter. This work was funded by Natural Environment Research Council (NERC; award NE/R000859/1 and award NE/R016429/1 as part of the UK-SCaPE programme delivering National Capability), Norwegian Research Council (SFF-III grant 223257), NTNU, UK Royal Society, Marine Alliance for Science and Technology for Scotland (MASTS), SOC and UoA.

Data Availability Statement

Data and code are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.3j9kd51mn.

Online enhancements:supplemental PDF


  • disruptive selection
  • multistate capture-recapture
  • partial migration
  • phenotypic plasticity
  • temporally varying selection
  • threshold trait


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