Independent Researcher, Montréal, Canada.
Biol Rev Camb Philos Soc. 2019 Dec;94(6):1918-1934. doi: 10.1111/brv.12540. Epub 2019 Jul 3.
Vigilance allows animals to monitor their surroundings for signs of danger associated with predators or rivals. As vigilance is costly, models predict that it should increase when the risk posed by predators or rivals increases. In addition, vigilance is expected to decrease in larger groups that provide more safety against predators. Risk and group size are thus two key determinants of vigilance. Together, they could have additive or interactive effects. If risk and group size interacted, the magnitude of the group-size effect on vigilance would vary depending on the level of risk experienced, implying that the benefits of sociality in terms of vigilance vary with risk. Depending on the model, vigilance is predicted to decrease more rapidly with group size at low risk or at high risk. Little work has focused directly on the interaction between risk and group size, making it difficult to understand under which conditions particular interactive effects arise and whether interactive effects are common in natural systems. I review the vast literature on vigilance in birds and mammals to assess whether interactive effects between risk and group size are common, and if present, which pattern occurs more frequently. In studies involving predation risk, the greatest proportion reported no statistically significant interactive effects. In other cases, vigilance decreased with group size more rapidly at low or high risk in a similar proportion of studies. In studies involving risk posed by rivals (social risk), most documented a more rapid decrease in vigilance with group size at low than at high risk, as predicted if the need to monitor rivals increases in larger groups. Low statistical power to detect interactive effects might have been an issue in several studies. The absence of interactive effects, on the other hand, might suggest constraints or limits on the ability of animals to adjust vigilance to current risk or group sizes. Interactive effects on vigilance have implications for the evolution of sociality and for our understanding of the phenotypic plasticity of predator- and competitor-induced defences and deserve more attention in future studies.
警戒使动物能够监测周围环境，以发现与捕食者或竞争对手相关的危险迹象。由于警戒是有代价的，因此模型预测，当捕食者或竞争对手带来的风险增加时，警戒应该会增加。此外，在提供更多针对捕食者安全保障的较大群体中，警戒预计会降低。因此，风险和群体大小是警戒的两个关键决定因素。它们共同作用，可能具有相加或交互作用。如果风险和群体大小相互作用，那么群体大小对警戒的影响幅度将取决于所经历的风险水平，这意味着社交在警戒方面的好处因风险而异。根据模型，在低风险或高风险的情况下，警戒随群体大小的减少速度预计会更快。很少有工作直接关注风险和群体大小之间的相互作用，因此很难了解在哪些条件下会出现特定的相互作用，以及相互作用是否在自然系统中普遍存在。我回顾了关于鸟类和哺乳动物警戒的大量文献，以评估风险和群体大小之间的相互作用是否常见，如果存在，哪种模式更为常见。在涉及捕食风险的研究中，报告没有统计学意义上的显著相互作用的比例最大。在其他情况下，在类似比例的研究中，在低风险或高风险的情况下，警戒随群体大小的减少速度更快。在涉及竞争对手（社会风险）带来的风险的研究中，大多数研究记录到，在较大的群体中，与高风险相比，在低风险时，警戒随群体大小的下降速度更快，如果在较大的群体中需要监视竞争对手的情况增加，则会出现这种情况。在某些研究中，检测交互作用的统计能力可能较低。另一方面，交互作用的缺失可能表明动物调整警戒以适应当前风险或群体大小的能力受到限制或限制。警戒的交互作用对社会性的进化以及对捕食者和竞争者引起的防御的表型可塑性的理解具有重要意义，值得在未来的研究中给予更多关注。
