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Data from: Cooperative breeding in birds increases the within-year fecundity mean without increasing the variance: A potential mechanism to buffer environmental uncertainty

Data files

Apr 16, 2025 version files 2.30 MB

Abstract

Cooperative breeding is a common strategy of vertebrates under harsh, unpredictable environments. Yet we do not fully understand the demographic mechanisms by which these species buffer environmental challenges, because while cooperation typically increases the fitness mean, whether it alters the variance to further reduce the population risk of stochastic extinction is unclear. We addressed this issue using a meta-analysis among avian cooperative breeders. Compared with their non-cooperative counterparts in the same populations, cooperative pairs on average fledged more offspring, without increasing the fecundity variance accordingly. This pattern held when failed nests were excluded from analysis to filter the effect of nest predation on the estimation of brood size at fledging, retaining the effect of brood reduction (the partial loss of nestlings in a brood). Cooperative pairs did not differ in the mean and variance of clutch size from non-cooperative pairs; the former had a lower level of brood reduction than the latter. These results suggest that mitigating brood reduction by cooperation is a pathway that may explain the observed pattern in the fecundity mean and variance. Our work highlights the importance of formulating the mean-variance relationship for fecundity to understand the evolutionary success of cooperative breeding.