Department of Biological Sciences, University of Denver, Denver, CO, USA.
Ecol Lett. 2018 Jan;21(1):138-150. doi: 10.1111/ele.12874. Epub 2017 Nov 2.
Primary consumers are under strong selection from resource ('bottom-up') and consumer ('top-down') controls, but the relative importance of these selective forces is unknown. We performed a meta-analysis to compare the strength of top-down and bottom-up forces on consumer fitness, considering multiple predictors that can modulate these effects: diet breadth, feeding guild, habitat/environment, type of bottom-up effects, type of top-down effects and how consumer fitness effects are measured. We focused our analyses on the most diverse group of primary consumers, herbivorous insects, and found that in general top-down forces were stronger than bottom-up forces. Notably, chewing, sucking and gall-making herbivores were more affected by top-down than bottom-up forces, top-down forces were stronger than bottom-up in both natural and controlled (cultivated) environments, and parasitoids and predators had equally strong top-down effects on insect herbivores. Future studies should broaden the scope of focal consumers, particularly in understudied terrestrial systems, guilds, taxonomic groups and top-down controls (e.g. pathogens), and test for more complex indirect community interactions. Our results demonstrate the surprising strength of forces exerted by natural enemies on herbivorous insects, and thus the necessity of using a tri-trophic approach when studying insect-plant interactions.
初级消费者受到资源（“底向上”）和消费者（“顶向下”）控制的强烈选择，但这些选择性力量的相对重要性尚不清楚。我们进行了荟萃分析，比较了顶向下和底向上力量对消费者适应性的影响强度，同时考虑了多种可以调节这些影响的预测因子：饮食广度、摄食群、栖息地/环境、底向上效应的类型、顶向下效应的类型以及如何衡量消费者适应性的影响。我们将分析重点放在最具多样性的初级消费者群体——草食性昆虫上，发现一般来说，顶向下力量比底向上力量更强。值得注意的是，咀嚼、吸食和造瘿的草食性昆虫受到的顶向下影响大于底向上影响，无论是在自然环境还是受控（栽培）环境中，顶向下力量都比底向上力量更强，寄生蜂和捕食者对昆虫草食性动物的顶向下效应同样强烈。未来的研究应该扩大焦点消费者的范围，特别是在研究较少的陆地系统、摄食群、分类群和顶向下控制（例如病原体）方面，并测试更复杂的间接群落相互作用。我们的结果表明，天敌对草食性昆虫施加的力量惊人地强大，因此在研究昆虫-植物相互作用时，有必要采用三营养级方法。
