Data from: Trophic interactions in an ant nest microcosm: a combined experimental and stable isotope (δ13C/δ15N) approach

Living in close association with other organisms has proven to be a widespread and successful strategy in nature. Some communities are completely driven by symbiotic associations and therefore, intimate relationships among the partners can be expected. Here, we analyzed in-depth the food web of a particularly rich community of arthropods found in strict association with European red wood ants (Formica rufa group). We studied the trophic links between different ant-associated myrmecophiles and food sources associated with the host ant, but also tested predator–prey links among myrmecophiles themselves. Our approach combined direct feeding tests and stable carbon and nitrogen isotope analyses for a large number of myrmecophiles. The results of the direct feeding tests reveal a complex food web. Most myrmecophiles were found to parasitize on ant brood. Moreover, we encountered multiple trophic predator– prey links among the myrmecophiles. The results of the stable isotope analyses complement these findings and indicate the existence of multiple trophic levels and trophic isotopic niche compartmentalization. δ15N values were strongly correlated with the trophic levels based on the direct tests, reflecting that δ15N values of myrmecophiles increased with higher trophic levels. This strong correlation underlines the strength of stable isotopes as a powerful tool to assess trophic levels. In addition, the stable isotope data suggest that most species only facultatively prey on ant brood. The presence of numerous trophic interactions among symbionts clearly contrasts with the traditional view of social insects nests as offering an enemy-free space for symbionts. Interestingly, the ant host can indirectly benefit from these interactions because brood predators are also preyed upon by other myrmecophiles. Overall, this study provides unique insights into the complex interactions in a small symbiont microcosm system and suggests that the interactions between host and symbiont might be mediated by other symbionts in the same community.

与其他生物形成紧密关联，已被证实是自然界中广泛存在且行之有效的生存策略。部分生物群落完全由共生关联所驱动，因此其成员间可预期存在紧密的依存关系。本研究针对与欧洲红褐林蚁（Formica rufa group）形成严格共生关系的物种格外丰富的节肢动物群落，深入解析其食物网结构。本研究不仅探讨了各类与蚂蚁共生的蚁栖生物（myrmecophiles）与寄主蚂蚁相关食物源之间的营养联系，同时也检测了蚁栖生物内部的捕食-被捕食营养关联。研究方法结合了针对大量蚁栖生物的直接摄食实验与稳定碳、氮同位素分析。直接摄食实验的结果显示该食物网结构极为复杂：绝大多数蚁栖生物均寄生于寄主蚂蚁的幼体；此外，研究还发现蚁栖生物内部存在多条跨营养级的捕食-被捕食关联。稳定同位素分析的结果对上述发现形成了补充，表明该群落存在多个营养层级，且存在营养同位素生态位分隔现象。基于直接实验得出的营养层级与蚁栖生物的δ15N值呈现显著相关性，这表明蚁栖生物的δ15N值会随其所处营养层级的提升而升高。这一强相关性进一步证实了稳定同位素作为评估营养层级的有效工具的可靠性。此外，稳定同位素数据显示，多数蚁栖生物仅兼性捕食寄主蚂蚁的幼体。共生体间存在大量营养级交互的现象，与传统观点形成鲜明对比——传统观点认为社会性昆虫的巢穴可为共生体提供无天敌的生存空间。值得注意的是，寄主蚂蚁可通过这些交互间接获益：因为捕食蚁幼体的生物，本身也会被其他蚁栖生物所捕食。综上，本研究为小型共生体微观系统中的复杂交互关系提供了独到见解，并表明寄主与共生体之间的交互作用，可能由同群落内的其他共生体所介导。