Data from: Do differences in food web structure between organic and conventional farms affect the ecosystem service of pest control?

While many studies have demonstrated that organic farms support greater levels of biodiversity, it is not known whether this translates into better provision of ecosystem services. Here we use a food-web approach to analyse the community structure and function at the whole-farm scale. Quantitative food webs from 10 replicate pairs of organic and conventional farms showed that organic farms have significantly more species at three trophic levels (plant, herbivore and parasitoid) and significantly different network structure. Herbivores on organic farms were attacked by more parasitoid species on organic farms than on conventional farms. However, differences in network structure did not translate into differences in robustness to simulated species loss and we found no difference in percentage parasitism (natural pest control) across a variety of host species. Furthermore, a manipulative field experiment demonstrated that the higher species richness of parasitoids on the organic farms did not increase mortality of a novel herbivore used to bioassay ecosystem service. The explanation for these differences is likely to include inherent differences in management strategies and landscape structure between the two farming systems.尽管诸多研究已证实，有机农场能够维持更高水平的生物多样性（biodiversity），但目前尚不明确这一优势是否能转化为生态系统服务的更优供给。本研究采用食物网方法（food-web approach），对全农场尺度的群落结构与功能展开分析。我们对10组重复配对的有机农场与常规农场的定量食物网（quantitative food web）进行分析，结果显示：有机农场在植物、植食者与拟寄生者（parasitoid）三个营养级（trophic level）上的物种数均显著更高，且群落网络结构存在显著差异。有机农场中的植食者所遭遇的拟寄生者物种数，显著多于常规农场的植食者。然而，网络结构的差异并未转化为模拟物种丧失后的群落鲁棒性差异；同时，在多种寄主物种中，我们未发现寄生率（即自然害虫防控能力）存在显著差异。此外，控制性野外实验（manipulative field experiment）结果表明，有机农场中拟寄生者物种丰富度更高这一特点，并未提升用于生态系统服务生物测定（bioassay）的新型植食者的死亡率。上述差异的潜在成因，可能包含两种农业系统在管理策略与景观结构上的固有差异。