Department of Biology, Wesleyan University, Middletown, CT, USA.
Department of Entomology, Washington State University, Pullman, WA, USA.
Ecol Lett. 2019 Oct;22(10):1599-1607. doi: 10.1111/ele.13352. Epub 2019 Jul 26.
Interactions between ants and phloem-feeding herbivores are characterised as a keystone mutualism because they restructure arthropod communities and generate trophic cascades. Keystone interactions in terrestrial food webs are hypothesised to depend on herbivore community structure and bottom-up effects on plant growth. Here, we tested this prediction at a landscape scale with a long-term ant-exclusion experiment on hickory saplings in the context of spatial variation in herbivore community structure and habitat quality. We quantified top-down effects of ants, herbivore communities as well as abiotic factors impacting hickory shoot growth. We found that ants influenced shoot growth via strong, context-dependent, compensatory effects, with clear cascading benefits only when phloem-feeders were present and chewing herbivore abundance was high. By contrast, while several landscape variables predicted hickory growth, they did not mediate the strength of cascading effects of ants. These results suggest that ant/sap-feeder mutualisms may regulate forest productivity by mediating effects of multiple herbivore guilds.
蚂蚁和韧皮部取食的草食性昆虫之间的相互作用被认为是一种关键共生关系，因为它们改变了节肢动物群落的结构，并产生了营养级联。陆地食物网中的关键相互作用被假设依赖于草食性昆虫群落的结构和对植物生长的自上而下的影响。在这里，我们在一个长期的山核桃树苗的蚂蚁排除实验中，在草食性昆虫群落结构和栖息地质量的空间变化的背景下，在景观尺度上测试了这一预测。我们量化了蚂蚁、草食性昆虫群落以及影响山核桃嫩枝生长的非生物因素的自上而下的影响。我们发现，蚂蚁通过强烈的、依赖于环境的补偿效应来影响嫩枝的生长，只有在韧皮部取食者存在且咀嚼性草食者数量较高时，才会产生明显的级联效益。相比之下，尽管有几个景观变量可以预测山核桃的生长，但它们并不能调节蚂蚁级联效应的强度。这些结果表明，蚂蚁/韧皮部食者共生关系可能通过调节多个草食性昆虫类群的作用来调节森林生产力。
