Data from: Group size adjustment to ecological demand in a cooperative breeder

Environmental factors can determine which group size will maximise the fitness of group members. This is particularly important in cooperative breeders, where group members often serve different purposes. Experimental studies are yet lacking to check whether ecologically mediated need for help will change the propensity of dominant group members to accept immigrants. Here we manipulated the perceived risk of predation for dominant breeders of the cooperatively breeding cichlid fish Neolamprologus pulcher to test their response to unrelated and previously unknown immigrants. Potential immigrants were more readily accepted if groups were exposed to fish predators or egg predators than to herbivorous fish or control situations lacking predation risk. Our data are consistent with both risk dilution and helping effects. Egg predators were presented before spawning, which might suggest that the fish adjust acceptance rates also to a potential future threat. Dominant group members of N. pulcher apparently consider both present and future need of help based on ecological demand. This suggests that acceptance of immigrants and more generally, tolerance of group members on demand could be a widespread response to ecological conditions in cooperatively breeding animals.

环境因素可决定何种种群规模能够最大化种群成员的适合度。这一点在合作繁殖类群中尤为关键，因为此类群内成员通常承担各异的功能。目前仍缺乏相关实验研究，用以验证生态介导的帮助需求是否会改变优势种群成员接纳外来个体的倾向。本研究以合作繁殖的慈鲷科饰颊新亮丽鲷（Neolamprologus pulcher）的优势繁殖个体为对象，通过操控其感知到的捕食风险，测试其对无关且此前未接触过的外来个体的响应。结果显示，相较于暴露于植食性鱼类或无捕食风险的对照组环境，当种群暴露于鱼类捕食者或卵捕食者时，其对外来潜在个体的接纳率显著更高。本研究数据同时支持风险稀释效应与互助效应。实验中卵捕食者的刺激施加于产卵前阶段，这或许表明这类慈鲷会依据潜在的未来威胁调整对外来个体的接纳率。饰颊新亮丽鲷的优势种群成员显然会基于生态需求，同时考量当下与未来的帮助需求。该研究结果提示，接纳外来个体以及更广泛意义上的按需接纳种群成员，或许是合作繁殖动物针对生态条件的一种普遍响应策略。