Economy of scale: third partner strengthens a keystone ant-plant mutualism

While foundation species can stabilize ecosystems at landscape scales, their ability to persist is often underlain by keystone interactions occurring at smaller scales. Acacia drepanolobium is a foundation tree, comprising >95% of woody cover in East African black-cotton savanna ecosystems. Its dominance is underlain by a keystone mutualistic interaction with several symbiotic ant species in which it provides housing (swollen thorns) and carbohydrate-rich nectar from extra-floral nectaries (EFN). In return, it gains protection from catastrophic damage from mega-herbivores. Crematogaster mimosae is the ecologically dominant symbiotic ant in this system, also providing the highest protection services. In addition to tending EFN, C. mimosae tend scale insects for carbohydrate-rich honeydew. We investigated the role of scale insects in this specialized ant-plant interaction. Specifically, does this putatively redundant third partner strengthen the ant-plant mutualism by making the ant a ...尽管基础物种（foundation species）可在景观尺度上维持生态系统稳定，但其自身的存续能力往往依托于发生在更小尺度上的关键种间相互作用。镰荚金合欢（Acacia drepanolobium）是一类基础乔木，其在东非黑棉土稀树草原生态系统的木本覆盖占比超过95%。该物种的优势地位，源自其与多种共生蚁类之间的关键互利共生关系：金合欢为蚁类提供栖息结构（膨大刺）以及源自花外蜜腺（extra-floral nectaries，EFN）的富碳水化合物花蜜。作为交换，蚁类则为其抵御大型草食动物带来的毁灭性破坏。含羞草举腹蚁（Crematogaster mimosae）是该系统中生态优势度最高的共生蚁类，同时能够提供最优的保护服务。除了照料花外蜜腺之外，含羞草举腹蚁还会抚育介壳虫以获取其分泌的富碳水化合物蜜露。本研究探究了介壳虫在这一特化蚁植共生关系中的作用。具体而言，这一被认为具备冗余性的第三伙伴，是否能够通过让蚁类……