Cooperative work in social birds: how is a tragedy of the commons averted?

合作行为的进化是进化生物学中一个基本而持久的问题。自然选择预计会选择自私的行为，因为个体应该寻求最大化自己的生殖成功，以便在下一代留下更多的后代。因此，当个人在共同的任务中合作时，不可避免地会在每个人应该努力工作的问题上产生冲突：每个人都希望别人工作得更努力，自己做得更少。因此，在社会群体中，合作行为很容易受到自私的个人或吃白食的人的剥削。公共产品博弈抓住了这一悖论的本质：由合作的个人组成的群体应该在竞争中胜过由自私的个人组成的群体，但自私的个人比群体内的合作个体做得更好。这种社会困境被称为公地悲剧，几乎存在于所有生物系统中，包括人类社会，过度开发鱼类种群等公共资源或未能遏制碳排放就是明显的例子。大量的理论文献表明，在大多数情况下，自私取代了合作，但在某些情况下，合作行为可能会保持下去。这些措施包括：1.不合作的个人通过执行制度受到惩罚或被迫合作。2.当个人必须通过合作获得良好声誉时，才能使自己的健康最大化。3.合作惠及亲属，使合作者通过亲属选择获得健康利益。这项研究的目的是利用南部非洲独特的群居编织者的公共繁殖系统来检验这些替代假设，以解决公地悲剧。这种善于交际的编织者建造了巨大的公共巢，其中一个巢群为多达数百只鸟提供了栖息和繁殖的场所。公共鸟巢有两个不同但完整的组成部分：具有支持和调节体温功能的茅草圆顶；以及嵌入茅草下的单个巢室，成对或小群的个体在其中栖息和繁殖。一个关键特征是，穹顶不是一种自组织结构，因为它不是投资于个别鸟巢房间的紧急资产。因此，蜂群成员必须投入时间和精力来建造和维护共同的圆顶和自己的巢室。善于交际的编织者如何解决个人之间关于合作投资的冲突，并避免导致社会崩溃的公地悲剧？这项研究将首先确定群体成员对公共产品的个人贡献，并确定这种努力是否代价高昂。公共产品的功能也将通过将茅草的温度调节特性与其大小和巢室的位置联系起来进行量化。最后，也是最重要的是，这项研究将通过实地观察和实验来检验，是否通过与亲属合作、通过其他群体成员执行合作工作来避免公地悲剧，或者因为合作工作是向其他群体成员发出个人质量的信号，并与个人自身的生殖成功相关。以前对社会性编织者的研究表明，研究计划是容易处理的，项目目标是可以实现的。这项研究将与开普敦大学珀西·菲茨帕特里克非洲鸟类学研究所合作，在南非金伯利的一个既定研究种群中进行。由于公地悲剧在生物系统中无处不在，这项研究的结果将在广泛的学科范围内具有广泛的相关性。

The evolution of cooperative behaviour is a fundamental and persistent problem in evolutionary biology. Natural selection is expected to select for selfish behaviour because individuals should seek to maximise their own reproductive success to leave more offspring in the next generation. Therefore, when individuals cooperate in joint tasks, there is inevitably conflict over how hard each should work: every individual would like others to work harder and to do less themselves. Hence, in social groups, cooperative behaviour will be vulnerable to exploitation by selfish individuals, or freeloaders. Public goods games capture the essence of the paradox: groups composed of cooperating individuals should out-compete groups of selfish individuals, but selfish individuals do better than cooperative ones within groups. This social dilemma is known as the tragedy of the commons and it is found in virtually all biological systems, including human societies, where over-exploitation of common resources such as fish stocks or failure to curb carbon emissions are obvious examples. An extensive theoretical literature shows that selfishness replaces cooperation under most conditions, but that cooperative behaviour may be maintained under certain circumstances. These include: 1. When non-cooperating individuals are punished or coerced into cooperation through a system of enforcement. 2. When individuals must achieve a good reputation through cooperation in order to maximise their own fitness. 3. When cooperation benefits relatives so that cooperators gain fitness benefits through kin selection. The aim of this study is to use the unique communal breeding system of the sociable weaver of southern Africa to test these alternative hypotheses for resolution of a tragedy of the commons. The sociable weaver builds massive communal nests in which a single nest mass provides roosting and breeding sites for up to several hundred birds. The communal nest has two distinct but integrated components: a thatched dome that has a supportive and thermoregulatory function; and individual nest chambers embedded beneath the thatch in which pairs or small groups of individuals roost and breed. A key feature is that the dome is not a self-organising structure because it is not an emergent property of investment in individual nest chambers. Thus, colony members must invest time and effort in building and maintaining the communal dome as well as their own nest chamber. How do sociable weavers resolve the conflict among individuals over cooperative investment and avoid a tragedy of the commons that would result in social collapse? This study will first determine the individual contributions made by colony members to public goods, and determine whether this effort is costly. The function of the public goods will also be quantified by relating the thermoregulatory properties of the thatch to its size and the position of nest chambers. Finally, and most importantly, this study will use field observations and experiments to test whether a tragedy of the commons is averted by cooperating with kin, through enforcement of cooperative work by other colony members, or because cooperative work is a signal to other colony members of an individual's quality with associated benefits to an individual's own reproductive success. Previous studies of sociable weavers show that the programme of research is tractable and the project's objectives achievable. The study will be conducted on an established study population of sociable weavers at Kimberley, South Africa, in collaboration with the Percy FitzPatrick Institute of African Ornithology at the University of Cape Town. Because of the ubiquity of the tragedy of the commons in biological systems, the findings of this study will have broad relevance across a wide range of disciplines.