Hatchwell B J
Am Nat. 1999 Aug;154(2):205-219. doi: 10.1086/303227.
An individual's optimal investment in young depends partly on the number of individuals caring for the same brood. In cooperative breeders, the investment strategy of parents with helpers is variable. When parents maintain the same effort regardless of helper number, helper care is additive. When parents fully compensate for the care of helpers by decreasing their own effort, total care does not increase. A study of long-tailed tits Aegithalos caudatus showed that both parental strategies may occur within a species, depending on the number of helpers. A comparative analysis of 27 cooperative breeders was conducted to test the predictions of a graphical model that care is additive when nestling starvation is frequent and parents exhibit compensatory reductions in care when starvation is rare. Both predictions were supported. In this interspecific comparison, a species' mean group size was not associated with compensatory responses by parents. There was some evidence that males and females had different investment rules. Males tended to show compensatory reductions in care when adult survival rate was low. In contrast, while both sexes showed compensation when nestling starvation was infrequent, this association was significant only for females.
个体在幼年期的最优投资部分取决于照顾同一窝幼雏的个体数量。在合作繁殖者中，有帮手的父母的投资策略是可变的。当父母无论帮手数量多少都保持相同的投入时，帮手的照顾是累加性的。当父母通过减少自己的投入来完全补偿帮手的照顾时，总的照顾量不会增加。一项对长尾山雀的研究表明，在一个物种内，这两种亲代策略都可能出现，具体取决于帮手的数量。对27种合作繁殖者进行了比较分析，以检验一个图形模型的预测，即当雏鸟饥饿频繁时，照顾是累加性的，而当饥饿罕见时，父母会表现出照顾的补偿性减少。这两个预测都得到了支持。在这种种间比较中，一个物种的平均群体规模与父母的补偿反应无关。有一些证据表明，雄性和雌性有不同的投资规则。当成年存活率较低时，雄性倾向于表现出照顾的补偿性减少。相比之下，虽然当雏鸟饥饿不频繁时，两性都会表现出补偿，但这种关联仅对雌性显著。
