Understanding the mechanisms contributing to positive relationships between predator diversity and natural pest control is fundamental to inform more effective management practices to support sustainable crop production. Predator body size can provide important insights to better understand and predict such predator-pest interactions. Yet, most studies exploring the link between predator body size and pest control have been conducted in species-poor communities under controlled environmental conditions, limiting our ability to generalize this relationship across heterogeneous landscapes. Using the community of naturally occurring ground beetles in cabbage fields, we examined how landscape composition (percent cropland) influences the size structure (mean, variance, and skewness of body size distribution) of predator communities and the subsequent effects on pest control. We found that predator communities shifted their size distribution toward larger body sizes in agriculturally dominated landscapes. This pattern arose from increasing numerical dominance of a few large-bodied species rather than an aggregated response across the community. Such landscape-driven changes in community size structure led to concomitant impacts on pest control, as the mean body size of predators was positively related to predation rates. Notably, the magnitude of pest control depended not only on the size of the dominant predators but was also strongly determined by the relative proportion of small vs. large-bodied species (i.e., skewness). Predation rates were higher in predator assemblages with even representation of small and large-bodied species relative to communities dominated by either large or small-bodied predators. Landscape composition may therefore modulate the relationship between predator body size and pest control by influencing the body size distribution of co-occurring species. Our study highlights the need to consider agricultural practices that not only boost effective predators, but also sustain a predator assemblage with a diverse set of traits to maximize overall pest control.

中文翻译：

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景观构成调节捕食者体型与害虫控制之间的关系


了解捕食者多样性与自然害虫控制之间的积极关系的机制对于提供更有效的管理实践以支持可持续作物生产至关重要。捕食者的体型可以提供重要的见解，以更好地理解和预测这种捕食者与害虫的相互作用。然而，大多数探索捕食者体型与害虫控制之间联系的研究都是在受控环境条件下的物种贫乏群落中进行的，这限制了我们在异质景观中推广这种关系的能力。利用卷心菜田中天然存在的地面甲虫群落，我们研究了景观组成（农田百分比）如何影响捕食者群落的大小结构（体型分布的平均值、方差和偏度）以及随后对害虫控制的影响。我们发现，在以农业为主的地区，捕食者群落的体型分布向更大的体型转变。这种模式是由于少数大型物种的数量优势不断增加而产生的，而不是整个群落的总体反应。这种景观驱动的群落规模结构变化对害虫控制产生了相应的影响，因为捕食者的平均体型与捕食率呈正相关。值得注意的是，害虫控制的程度不仅取决于主要捕食者的大小，而且很大程度上取决于小型与大型物种的相对比例（即偏度）。与以大型或小型捕食者为主的群落相比，小型和大型物种的捕食率更高。 因此，景观构成可能通过影响共生物种的体型分布来调节捕食者体型与害虫控制之间的关系。我们的研究强调需要考虑农业实践，不仅要增强有效的捕食者，还要维持具有多种性状的捕食者组合，以最大限度地全面控制害虫。