The dear enemy hypothesis predicts that territorial individuals will be less aggressive toward known neighbors than to strangers. This hypothesis has been well studied and there is a wealth of data demonstrating its prevalence in some taxa. However, a quantitative synthesis is needed to test the generality of the phenomenon, identify key mechanisms driving the behavior, and guide future research. In this study, we conduct a meta-analysis and, we test the importance of the location of intrusion, the type of experiment conducted (field, laboratory, or neutral arenas), and the sex and breeding status of territory holders, on the occurrence of dear enemy behavior. We also test how various ecological and life history traits, such as territory type, stimulus of intrusion, and taxonomic group, affect the magnitude of dear enemy behavior. We find that this phenomenon is common and that taxonomic class and breeding status are correlated with the expression of dear enemy behaviors. Further, we found that the way authors measure aggression influences the likelihood of identifying dear enemy responses, and thus we discuss potential pitfalls of dear enemy studies. Considering this conclusion, we discuss future lines of inquiry that could more directly examine the mechanisms of the dear enemy phenomenon.

亲爱的敌人假设预测领土个体对已知邻居的攻击性将低于对陌生人的攻击性。这个假设已经得到了很好的研究，并且有大量数据证明它在某些分类群中的流行。然而，需要进行定量综合来测试现象的普遍性，确定驱动行为的关键机制，并指导未来的研究。在这项研究中，我们进行了一项荟萃分析，我们测试了入侵地点、进行的实验类型（野外、实验室或中立场地）以及领地持有者的性别和繁殖状况对发生的重要性亲爱的敌人的行为。我们还测试了各种生态和生活史特征，如领土类型、入侵刺激和分类群，如何影响亲爱的敌人行为的程度。我们发现这种现象很常见，并且分类学类别和繁殖状态与亲爱的敌人行为的表达相关。此外，我们发现作者衡量攻击性的方式会影响识别敌对反应的可能性，因此我们讨论了敌对研究的潜在陷阱。考虑到这一结论，我们将讨论可以更直接地检验“亲爱的敌人”现象的机制的未来调查路线。