Female-biased sex ratios in urban centers create a "fertility trap" in post-war Finland

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Pettay , J E , Lummaa , V , Lynch , R & Loehr , J 2021 , ' Female-biased sex ratios in urban centers create a "fertility trap" in post-war Finland ' , Behavioral Ecology , vol. 32 , no. 4 , pp. 590-598 . https://doi.org/10.1093/beheco/arab007

Title: Female-biased sex ratios in urban centers create a "fertility trap" in post-war Finland
Author: Pettay, Jenni E.; Lummaa, Virpi; Lynch, Robert; Loehr, John
Contributor organization: Biological stations
Lammi Biological Station
Date: 2021
Language: eng
Number of pages: 9
Belongs to series: Behavioral Ecology
ISSN: 1045-2249
DOI: https://doi.org/10.1093/beheco/arab007
URI: http://hdl.handle.net/10138/334395
Abstract: Because sex ratios are a key factor regulating mating success and subsequent fitness both across and within species, there is widespread interest in how population-wide sex ratio imbalances affect marriage markets and the formation of families in human societies. Although most modern cities have more women than men and suffer from low fertility rates, the effects of female-biased sex ratios have garnered less attention than male-biased ratios. Here, we analyze how sex ratios are linked to marriages, reproductive histories, dispersal, and urbanization by taking advantage of a natural experiment in which an entire population was forcibly displaced during World War II to other local Finnish populations of varying sizes and sex ratios. Using a discrete time-event generalized linear mixed-effects model, and including factors that change across time, such as annual sex ratio, we show how sex ratios, reproduction, and migration are connected in a female-dominated environment. Young childless women migrated toward urban centers where work was available to women, and away from male-biased rural areas. In such areas where there were more females, women were less likely to start reproduction. Despite this constraint, women showed little flexibility in mate choice, with no evidence for an increase in partner age difference in female-biased areas. We propose that together these behaviors and conditions combine to generate an "urban fertility trap" which may have important consequences for our understanding of the fertility dynamics of today including the current fertility decline across the developed world.
Description: Correction DOI10.1093/beheco/arac030 Early Access APR 2022 Indexed 2022-05-02
Subject: dispersal
mate choice
sex ratio
1181 Ecology, evolutionary biology
Peer reviewed: Yes
Rights: cc_by
Usage restriction: openAccess
Self-archived version: publishedVersion

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