Strong survival selection on seasonal migration versus residence induced by extreme climatic events

• Published in: The Journal of animal ecology Vol. 90; no. 4; pp. 796 - 808
• Main Authors: Acker, Paul, Daunt, Francis, Wanless, Sarah, Burthe, Sarah J., Newell, Mark A., Harris, Michael P., Grist, Hannah, Sturgeon, Jenny, Swann, Robert L., Gunn, Carrie, Payo‐Payo, Ana, Reid, Jane M., Aubry, Lise
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-04-2021
• Subjects: Animal Migration; Animals; Bayesian capture–recapture; Birds; Breeding seasons; Capture-recapture studies; Changing environments; Climate Change; eco‐evolutionary dynamics; Evolution; extreme climatic events; Female; full annual cycle; Genetic diversity; Migration; Mortality; multi‐state model; partial migration; Phenotype; Phenotypic variations; Population; Population Dynamics; seasonal movement; Seasons; Sex; sex‐biased selection; Survival; Winter; Winter storms; Bayesian capture-recapture; multi-state model; extreme climatic events; eco-evolutionary dynamics; partial migration; full annual cycle; seasonal movement; sex-biased selection
• ISSN: 0021-8790; 1365-2656
• DOI: 10.1111/1365-2656.13410

Elucidating the full eco‐evolutionary consequences of climate change requires quantifying the impact of extreme climatic events (ECEs) on selective landscapes of key phenotypic traits that mediate responses to changing environments. Episodes of strong ECE‐induced selection could directly alter population composition, and potentially drive micro‐evolution. However, to date, few studies have quantified ECE‐induced selection on key traits, meaning that immediate and longer‐term eco‐evolutionary implications cannot yet be considered.
One widely expressed trait that allows individuals to respond to changing seasonal environments, and directly shapes spatio‐seasonal population dynamics, is seasonal migration versus residence. Many populations show considerable among‐individual phenotypic variation, resulting in ‘partial migration’. However, variation in the magnitude of direct survival selection on migration versus residence has not been rigorously quantified, and empirical evidence of whether seasonal ECEs induce, intensify, weaken or reverse such selection is lacking.
We designed full annual cycle multi‐state capture–recapture models that allow estimation of seasonal survival probabilities of migrants and residents from spatio‐temporally heterogeneous individual resightings. We fitted these models to 9 years of geographically extensive year‐round resighting data from partially migratory European shags Phalacrocorax aristotelis. We thereby quantified seasonal and annual survival selection on migration versus residence across benign and historically extreme non‐breeding season (winter) conditions, and tested whether selection differed between females and males.
We show that two of four observed ECEs, defined as severe winter storms causing overall low survival, were associated with very strong seasonal survival selection against residence. These episodes dwarfed the weak selection or neutrality evident otherwise, and hence caused selection through overall annual survival. The ECE that caused highest overall mortality and strongest selection also caused sex‐biased mortality, but there was little overall evidence of sex‐biased selection on migration versus residence.
Our results imply that seasonal ECEs and associated mortality can substantially shape the landscape of survival selection on migration versus residence. Such ECE‐induced phenotypic selection will directly alter migrant and resident frequencies, and thereby alter immediate spatio‐seasonal population dynamics. Given underlying additive genetic variation, such ECEs could potentially cause micro‐evolutionary changes in seasonal migration, and thereby cause complex eco‐evolutionary population responses to changing seasonal environments.
The authors quantify the seasonal survival selection landscape of migration versus residence over nine years in European shags. Using multi‐state capture–recapture models fitted to geographically extensive resighting data, they find two major episodes of selection against residence that coincide with extreme climatic events and contrast with weak selection or neutrality evident otherwise. (Photo by Mark A. Newell)