The Benefits of Help in Cooperative Birds – non-existent or difficult to detect?

In birds that breed cooperatively in family groups, adult offspring often
delay dispersal to assist the breeding pair in raising their
young. Kin selection is thought to play an important role in the
evolution of this breeding system. However, evidence supporting the
underlying assumption that helpers increase the reproductive success of
breeders is inconsistent. In 10/19 species where the effect of
helpers on breeder reproductive success has been estimated while
controlling for the effects of breeder and territory quality, no benefits
of help were detected. Here we use phylogenetic meta-analysis to show that
the inconsistent evidence for helper benefits across species is explained
by study design. After accounting for low sample sizes and the different
study designs used to control for breeder and territory quality, we found
that helpers consistently enhanced the reproductive success of breeders.
Therefore, the assumption that helpers increase breeder reproductive
success is supported by evidence across cooperatively breeding birds.

在以家族群体形式进行合作繁殖的鸟类中，成年后代常延迟扩散（dispersal）以协助繁殖对抚育幼鸟。亲属选择（kin selection）被认为在该繁殖系统的演化中发挥重要作用。然而，支持“帮助者可提升繁殖者繁殖成功率”这一核心假设的证据并不一致：在19个已评估帮助者对繁殖者繁殖成功率影响（同时控制繁殖者质量与领域质量效应）的物种中，有10个未检测到帮助的益处。本研究通过系统发育元分析（phylogenetic meta-analysis）表明，跨物种间帮助者益处证据的不一致性可由研究设计解释。在考虑样本量不足及用于控制繁殖者与领域质量的不同研究设计后，我们发现帮助者持续提升繁殖者的繁殖成功率。因此，“帮助者可提高繁殖者繁殖成功率”的假设在合作繁殖鸟类中得到了跨物种证据的支持。