Data for: Complex battlefields favor strong soldiers over large armies in social animal warfare

In social animals, success can depend on the outcome of group battles. Theoretical models of warfare predict that group fighting ability is proportional to two key factors: the strength of each soldier in the group and group size. The relative importance of these factors is predicted to vary across environments [F. W. Lanchester, Aircraft in Warfare, the Dawn of the Fourth Arm (1916)]. Here, we provide an empirical validation of the theoretical prediction that open environments should favor superior numbers, whereas complex environments should favor stronger soldiers [R. N. Franks, L. W. Partridge, Anim. Behav. 45, 197–199 (1993)]. We first demonstrate this pattern using simulated battles between relatively strong and weak soldiers in a computer-driven algorithm. We then validate this result in real animals using an ant model system: In battles in which the number of strong native meat ant Iridomyrmex purpureus workers is constant while the number of weak non-native invasive Argentine ant Linepithema humile workers increases across treatments, fatalities of I. purpureus are lower in complex than in simple arenas. Our results provide controlled experimental evidence that investing in stronger soldiers is more effective in complex environments. This is a significant advance in the empirical study of nonhuman warfare and is important for understanding the competitive balance among native and non-native invasive ant species.

在社会性动物中，群体的生存成败往往取决于群体战斗的结果。群体作战的理论模型预测，群体的战斗能力与两个关键因素成正比：群体中每个作战个体的实力，以及群体规模。据预测，这两个因素的相对重要性会随环境不同而发生变化[F. W. 兰彻斯特，《作战中的飞行器：第四兵种的诞生》(1916)]。本研究针对该理论预测开展实证验证：开阔环境更青睐数量优势，而复杂环境则更偏向于实力更强的作战个体[R. N. 弗朗克斯、L. W. 帕特里奇，《动物行为（Anim. Behav.）》，45卷，197–199页(1993)]。我们首先借助计算机算法驱动的强弱作战个体模拟战斗，验证了该规律。随后我们以蚂蚁作为模式生物体系，在真实动物群体中验证了这一结果：在实验中，实力较强的本土肉蚁（Iridomyrmex purpureus）工蚁数量保持恒定，而实力较弱的外来入侵阿根廷蚁（Linepithema humile）工蚁数量随实验处理组递增，结果显示，复杂实验场地中本土肉蚁的死亡率低于简单实验场地。本研究的结果提供了可控实验证据，证明在复杂环境中，投入实力更强的作战个体更为有效。该研究在非人类作战的实证研究领域取得了重要进展，同时对于理解本土与外来入侵蚁类物种间的竞争平衡具有重要意义。