Data from: Individual dispersal decisions in a cooperative breeder: ecological constraints, the benefits of philopatry, and the social queue for dominance

1. Delayed dispersal is a key step in the evolution of familial animal societies and cooperative breeding. However, no consensus has been reached on the ecological and social circumstances driving delayed dispersal. 2. Here we test predictions from the ecological constraints and benefits of philopatry hypotheses as well as the recently-proposed dual benefits hypothesis to better understand the evolution of group-living and cooperative breeding. Furthermore, we consider how individual social circumstances within groups affect dispersal decisions. 3. We examine 11 years of life-history information on a wild population of cooperatively breeding southern pied babblers (Turdoides bicolor). We investigate the effects of ecological conditions, natal-group membership and individual social context on male and female dispersal delays, disperser survival and acquisition of dominance. 4. Female dispersal decisions are generally unconstrained by ecological or social circumstances. In contrast, males disperse in response to relaxed ecological constraints, decreases in nepotistic tolerance, or when low social rank in the queue for dominance decreases their likelihood of gaining a dominant breeding position. Early dispersal by end-of-queue males often leads to a head-of-queue subordinate position in a non-natal group, thereby increasing access to dominant breeding positions. However, males and females remaining in natal groups gain benefits of philopatry via increased survival and, for head-of-queue males, very high likelihood of acquisition of a breeding position. 5. Overall, predictions from the dual benefits hypothesis best describe these results, while some predictions from each of the ecological constraints and benefits of philopatry hypotheses were supported. The benefits of living and working together (collective action benefits) in large stable groups are of central importance in shaping dispersal delays in southern pied babbler societies. In addition, position in the subordinate social queue for dominance is key in determining access to reproduction, particularly for males. This research highlights the importance of considering the costs and benefits of individual social circumstances in dispersal decisions and illustrates how the dual benefits hypothesis offers new perspectives in understanding delayed dispersal.

1. 延迟扩散（delayed dispersal）是动物家族社会与合作繁殖（cooperative breeding）演化的关键环节，但目前学界对于驱动延迟扩散的生态与社会环境尚未达成共识。
2. 本研究针对生态限制假说（ecological constraints hypothesis）、恋家收益假说（benefits of philopatry hypothesis），以及新近提出的双重收益假说（dual benefits hypothesis）展开预测检验，以深入解析群居生活与合作繁殖的演化机制。此外，我们还探讨了群体内个体的社会环境如何影响扩散决策。
3. 本研究分析了合作繁殖的野生南非斑鸫鹛（Turdoides bicolor）种群长达11年的生活史数据，探讨了生态条件、出生群体归属以及个体社会背景对雌雄个体扩散延迟时长、扩散者存活率以及优势地位获得的影响。
4. 雌性个体的扩散决策通常不受生态或社会环境的约束。与之相反，雄性个体在生态限制放松、亲缘宽容度下降时，或是在优势地位顺位队列中处于低位、难以获得优势繁殖地位时，会选择扩散。顺位末尾的雄性提前扩散后，往往能在非出生群体中成为顺位首位的从属个体，进而提升其获得优势繁殖地位的概率。而留在出生群体中的雌雄个体，则可通过更高的存活率获得恋家收益；对于顺位首位的雄性而言，还能拥有极高的繁殖地位获得概率。
5. 总体而言，双重收益假说的预测最贴合本研究结果，同时生态限制假说与恋家收益假说的部分预测也得到了验证。在大型稳定群体中，共同生活与协作带来的集体行动收益（collective action benefits）是塑造南非斑鸫鹛社会中延迟扩散行为的核心因素。此外，从属个体的优势地位顺位队列位置是决定繁殖机会的关键，这一点在雄性个体中尤为明显。本研究强调了在探讨扩散决策时需考虑个体社会环境的成本与收益，并阐明了双重收益假说为理解延迟扩散行为提供了全新视角。