Clark Robert E, Singer Michael S
Biology Department, Wesleyan University, Middletown, CT, USA.
Oecologia. 2018 Mar;186(3):601-610. doi: 10.1007/s00442-017-4047-5. Epub 2018 Jan 6.
Determining the impacts of mutualistic interactions and predator diversity on food webs are two important goals in community ecology. In this study, we examined how predator community variation mediates the strength of top-down effects in the presence and absence of mutualistic interactions. We examined the impacts of predatory ant species that simultaneously prey on leaf-chewing herbivores (Lepidoptera) and engage in food-for-protection mutualisms with sap-feeding herbivores (Hemiptera) in the lower canopy of Connecticut forests. In this 2-year study, we examined three hypothetical mechanisms by which mutualisms can alter the top-down effects of ants: (1) sap feeders increase ant abundance, thus strengthening predatory effects; (2) sap feeders increase the relative abundance of a species that has stronger predatory effects; and (3) changes to predator diversity (species richness) are caused by sap feeders mediating top-down effects of the ant community. Experiments revealed that host plants occupied by sap feeders favored large-bodied ant species in the genus Camponotus, but there were no changes to community-wide ant abundance or ant species richness. Fitting predictions of predation strength based on the functional trait of body size, large-bodied Camponotus suppressed caterpillars and reduced leaf herbivory. This work shows that the ant-hemipteran mutualism, which has been characterized as a keystone interaction, can generate strong top-down effects on leaf-chewing herbivores and herbivory via increasing the relative abundance of species with functional traits relevant to predation, such as body size. Therefore, the emergence of specific ants as keystone predators in a community can be contingent upon their mutualism with sap-feeding Hemiptera.
确定互利共生相互作用和捕食者多样性对食物网的影响是群落生态学中的两个重要目标。在本研究中，我们研究了在存在和不存在互利共生相互作用的情况下，捕食者群落变化如何介导自上而下效应的强度。我们研究了捕食性蚂蚁物种的影响，这些蚂蚁既捕食咀嚼叶片的食草动物（鳞翅目），又与康涅狄格森林下层吸食树液的食草动物（半翅目）进行食物换保护的互利共生。在这项为期两年的研究中，我们研究了互利共生可以改变蚂蚁自上而下效应的三种假设机制：（1）吸食树液者增加蚂蚁数量，从而增强捕食效应；（2）吸食树液者增加具有更强捕食效应的物种的相对丰度；（3）吸食树液者介导蚂蚁群落的自上而下效应，从而导致捕食者多样性（物种丰富度）的变化。实验表明，有吸食树液者占据的寄主植物有利于弓背蚁属中的大型蚂蚁物种，但整个群落的蚂蚁数量或蚂蚁物种丰富度没有变化。根据体型的功能特征对捕食强度进行拟合预测，大型弓背蚁抑制了毛虫并减少了叶片食草作用。这项工作表明，被视为关键相互作用的蚂蚁 - 半翅目互利共生，可以通过增加具有与捕食相关功能特征（如体型）的物种的相对丰度，对咀嚼叶片的食草动物和食草作用产生强烈的自上而下效应。因此，特定蚂蚁作为群落中的关键捕食者的出现可能取决于它们与吸食树液的半翅目的互利共生关系。
