Department of Entomology, University of Georgia, Athens, GA, USA.
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
J Anim Ecol. 2021 May;90(5):1341-1352. doi: 10.1111/1365-2656.13459. Epub 2021 Mar 12.
Interactions between herbivores and their predators are shaped, in part, by plant phenotype. Consequently, ubiquitous symbionts of plants below-ground, such as arbuscular mycorrhizal fungi (AMF), may influence interactions above-ground between predators and their prey by altering plant phenotype. However, the ecological relevance of below-ground organisms on predator-prey interactions under field conditions remains unclear. We assessed how AMF influence herbivore-predator interactions through a field experiment. We planted two milkweed species (Asclepias curassavica and Asclepias incarnata) provided with different amounts of AMF inoculum (zero, medium, and high) in a randomized block design. We added aphids to plants and reduced predator pressure weekly for 5 weeks to evaluate effects of AMF on predator recruitment. We then allowed herbivore-predator interactions to re-establish naturally for the remainder of the season to examine whether AMF-mediated variation in predator recruitment influenced the suppression of aphid populations. Arbuscular mycorrhizal fungi availability in soils mediated interactions between predaceous aphid midge flies Aphidoletes aphidimyza and their aphid prey Aphis nerii, but the effects were plant species-specific. On A. curassavica, by mid-season, midges were recruited most strongly on plants under medium AMF availability and least on plants under high AMF availability. In contrast, each midge killed fewer aphids with increasing aphid density on medium AMF plants, but killed more aphids with increasing aphid density on high AMF plants. In combination, aphid mortality rates imposed by midges were greatest on medium AMF plants, followed by high and zero AMF plants. By comparison, on A. incarnata, the recruitment of midges was strongest on high AMF plants and weakest on medium AMF plants. AMF had no effect on the number of aphids killed per midge, relative to aphid density, so mortality rates of aphids imposed by midges mirrored recruitment. Rates of decline in aphid populations following predator recolonization were associated with midge densities, as well as lacewing and syrphid densities, which were unaffected by AMF availability. Therefore, the effects of AMF on aphid population decline were not a simple function of AMF-midge interactions. Our findings demonstrate that the availability of AMF in soils has pervasive, but complex, effects on predator-herbivore dynamics in the field.
食草动物与其捕食者之间的相互作用部分受植物表型的影响。因此，植物地下普遍存在的共生体，如丛枝菌根真菌（AMF），可能通过改变植物表型，影响地上捕食者与其猎物之间的相互作用。然而，在野外条件下，地下生物对捕食者-猎物相互作用的生态相关性仍不清楚。我们通过野外实验评估了 AMF 如何影响食草动物-捕食者相互作用。我们在随机区组设计中种植了两种乳草物种（Asclepias curassavica 和 Asclepias incarnata），并提供了不同数量的 AMF 接种物（零、中、高）。我们向植物添加了蚜虫，并每周减少一次捕食者压力，持续 5 周，以评估 AMF 对捕食者招募的影响。然后，我们让食草动物-捕食者相互作用自然重新建立，以观察 AMF 介导的捕食者招募变化是否影响蚜虫种群的抑制。土壤中丛枝菌根真菌的可用性调节了捕食性蚜虫蝇 Aphidoletes aphidimyza 和它们的蚜虫猎物 Aphis nerii 之间的相互作用，但这种作用是特定于植物物种的。在 A. curassavica 上，到了季中，在中 AMF 可用性下，中最多的被招募到植物上，而在高 AMF 可用性下则最少。相比之下，随着蚜虫密度的增加，每只中杀死的蚜虫数量在中 AMF 植物上减少，但在高 AMF 植物上增加。综合起来，中对蚜虫的死亡率最高的是中 AMF 植物，其次是高 AMF 植物和零 AMF 植物。相比之下，在 A. incarnata 上，中最多的被招募到高 AMF 植物上，而在中 AMF 植物上最少。AMF 对每只中杀死的蚜虫数量相对于蚜虫密度没有影响，因此中对蚜虫的死亡率反映了招募情况。捕食者重新定植后蚜虫种群数量的下降速度与中密度以及草蛉和食蚜蝇密度有关，而 AMF 可用性对其没有影响。因此，AMF 对蚜虫种群下降的影响不是 AMF-中相互作用的简单函数。我们的研究结果表明，土壤中 AMF 的可用性对野外捕食者-猎物动态具有普遍但复杂的影响。
