Michener's group-size paradox in cooperatively breeding birds
Downing, Philip A. (2024-01-18)
John Wiley & Sons
18.01.2024
Philip A Downing, Michener’s group-size paradox in cooperatively breeding birds, Journal of Evolutionary Biology, Volume 37, Issue 3, March 2024, Pages 353–359, https://doi.org/10.1093/jeb/voae008
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© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Evolutionary Biology. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com
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© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Evolutionary Biology. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:oulu-202403042095
https://urn.fi/URN:NBN:fi:oulu-202403042095
Tiivistelmä
Abstract
According to Michener’s paradox, most altruistic groups in nature should be small and large groups should not exist. This is because per capita productivity is thought to decrease as groups get larger, meaning that the share of indirect fitness available to each group member declines, which favours dispersal. The empirical evidence for a decrease in per capita productivity is contradictory, however, and limited to the social Hymenoptera. I report that per capita reproductive success decreased with increasing group size across 26 cooperatively breeding bird species. Small groups comprising two or three individuals were the most common (79% of 16,101 groups), and these had the highest per capita reproductive success. This close fit between per capita reproductive success and the distribution of group sizes in nature suggests that it may indeed be difficult for large groups to evolve through indirect fitness benefits alone.
According to Michener’s paradox, most altruistic groups in nature should be small and large groups should not exist. This is because per capita productivity is thought to decrease as groups get larger, meaning that the share of indirect fitness available to each group member declines, which favours dispersal. The empirical evidence for a decrease in per capita productivity is contradictory, however, and limited to the social Hymenoptera. I report that per capita reproductive success decreased with increasing group size across 26 cooperatively breeding bird species. Small groups comprising two or three individuals were the most common (79% of 16,101 groups), and these had the highest per capita reproductive success. This close fit between per capita reproductive success and the distribution of group sizes in nature suggests that it may indeed be difficult for large groups to evolve through indirect fitness benefits alone.
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