Data from: Bottom-up vs. top-down effects on terrestrial insect herbivores: a meta-analysis

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 of a tri-trophic approach when studying insect-plant interactions.

初级消费者面临来自资源「自下而上（bottom-up）」调控与消费者「自上而下（top-down）」调控的强烈选择压力，但学界尚未明确这两类选择作用力的相对重要性。本研究开展了一项元分析（meta-analysis），以比较自上而下与自下而上作用力对消费者适合度的影响强度，同时纳入了多项可调控上述效应的预测因子：取食广度、取食功能群、生境/环境、自下而上效应类型、自上而下效应类型，以及消费者适合度效应的测量方式。本研究将分析聚焦于物种多样性最高的初级消费者类群——植食性昆虫，结果发现总体而言自上而下作用力的影响强度高于自下而上作用力。值得注意的是，咀嚼式、刺吸式与造瘿类植食性昆虫受到自上而下作用力的影响显著强于自下而上作用力；无论是自然环境还是受控（栽培）环境中，自上而下作用力的影响均强于自下而上作用力；而寄生性天敌与捕食性天敌对植食性昆虫的自上而下调控效应强度相当。未来的研究应当拓宽目标消费者类群的研究范围，尤其是在尚未被充分探索的陆地生态系统、取食功能群、分类类群以及自上而下调控因子（如病原物）中，并检验更为复杂的群落间接互作关系。本研究结果证实了天敌对植食性昆虫的调控作用力强度远超预期，因此在研究昆虫-植物互作时，采用三营养级（tri-trophic）研究范式具有必要性。