Data from: The curious case of the camelthorn: competition, coexistence and nest-site limitation in a multispecies mutualism

Myrmecophyte plants house ants in domatia in exchange for protection from herbivores. Ant-myrmecophyte mutualisms exhibit two general patterns due to competition between ants for plant occupancy: i) domatia nest-sites are a limiting resource and ii) each individual plant hosts one ant species at a time. However, individual camelthorn trees (Vachellia erioloba) typically host two to four ant species simultaneously, often coexisting in adjacent domatia on the same branch. Such fine-grain spatial coexistence questions the conventional wisdom on ant-myrmecophyte mutualisms. Camelthorn ants appear not to be nest-site limited, despite low abundance of suitable domatia, and have random distributions of nest-sites within and across trees. These patterns suggest a lack of competition between ants for domatia and contrast strongly with other ant-myrmecophyte systems. Comparison of this unusual case with others suggests that spatial scale is crucial to coexistence or competitive exclusion involving multiple ant species. Furthermore, coexistence may be facilitated when co-occurring ant species diverge strongly on at least one niche axis. Our conclusions provide recommendations for future ant-myrmecophyte research, particularly in utilising multispecies systems to further our understanding of mutualism biology.

蚁栖植物（Myrmecophyte）会为蚂蚁提供栖息于蚁巢体（domatia）的场所，以此换取蚂蚁为自身抵御植食动物的保护。因蚂蚁间争夺植物栖息权的竞争，蚁-蚁栖植物互利共生（mutualisms）体系通常呈现两种典型模式：其一，蚁巢体为限制性资源；其二，单株植物单次仅能宿主一种蚂蚁。然而，单株骆驼荆棘树（Vachellia erioloba）通常会同时容纳2至4种蚂蚁，且这些蚂蚁常共存于同一枝条上相邻的蚁巢体中。这种精细化的空间共存格局，对当前关于蚁-蚁栖植物互利共生的主流认知构成了挑战。尽管适宜的蚁巢体资源稀缺，但骆驼荆棘树的蚂蚁似乎并未受巢址资源限制，且其巢址在单株树内以及不同树木间均呈随机分布。这些特征表明，蚂蚁之间并不存在针对蚁巢体的竞争，这与其他蚁-蚁栖植物共生系统的情况形成强烈反差。将这一特殊案例与其他共生系统对比后可知，空间尺度在涉及多种蚂蚁的物种共存或竞争排斥过程中至关重要。此外，若共存的蚂蚁物种至少在一个生态位轴（niche axis）上存在显著分化，则更易实现物种共存。本研究结论为未来蚁-蚁栖植物相关研究提供了指导方向，尤其强调可借助多物种共生体系，进一步深化我们对互利共生生物学的认知。