Centre for Research in Animal Behaviour, Department of Psychology, Faculty of Health and Life Sciences, University of Exeter, Exeter, UK.
Proc Biol Sci. 2023 Jul 12;290(2002):20230790. doi: 10.1098/rspb.2023.0790.
The volunteer's dilemma, in which a single individual is required to produce a public good, predicts that individuals in larger groups will cooperate less frequently. Mechanistically, this could result from trade-offs between costs associated with volunteering and costs incurred if the public good is not produced (nobody volunteers). During predator inspection, one major contributor to the cost of volunteering is likely increased probability of predation; however, a predator also poses a risk to all individuals if nobody inspects. We tested the prediction that guppies in larger groups will inspect a predator less than those in smaller groups. We also predicted that individuals in larger groups would perceive less threat from the predator stimulus because of the protective benefits of larger groups (e.g. dilution). Contrary to prediction, we found that individuals in large groups inspected more frequently than those in smaller groups, but (as predicted) spent less time in refuges. There was evidence that individuals in intermediate-sized groups made fewest inspections and spent most time in refuges, suggesting that any link between group size, risk and cooperation is not driven by simple dilution. Extensions of theoretical models that capture these dynamics will likely be broadly applicable to risky cooperative behaviour.
志愿者困境，即个体需要生产公共物品，这一困境预测了在更大的群体中，个体合作的频率会降低。从机制上讲，这可能是由于与志愿服务相关的成本和如果不生产公共物品（没有人志愿）而产生的成本之间的权衡所致。在捕食者检查期间，志愿者的主要成本之一可能是被捕食的概率增加；然而，如果没有人检查，捕食者也会对所有个体构成威胁。我们测试了以下预测：与较小群体相比，较大群体中的孔雀鱼检查捕食者的次数更少。我们还预测，由于较大群体的保护效益（例如稀释效应），较大群体中的个体对捕食者刺激的感知威胁较小。与预测相反，我们发现，与较小群体相比，较大群体中的个体更频繁地进行检查，但（如预测的那样）在避难所中花费的时间更少。有证据表明，中等大小群体中的个体检查次数最少，在避难所中花费的时间最多，这表明群体大小、风险和合作之间的任何联系都不是由简单的稀释作用驱动的。捕捉这些动态的理论模型的扩展可能广泛适用于有风险的合作行为。
