Macfadyen Sarina, Gibson Rachel, Polaszek Andrew, Morris Rebecca J, Craze Paul G, Planqué Robert, Symondson William O C, Memmott Jane
School of Biological Sciences, University of Bristol, Woodland Road, Bristol, UK.
Ecol Lett. 2009 Mar;12(3):229-38. doi: 10.1111/j.1461-0248.2008.01279.x. Epub 2009 Jan 8.
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.
虽然许多研究表明有机农场能支持更高水平的生物多样性，但尚不清楚这是否能转化为更好地提供生态系统服务。在此，我们采用食物网方法来分析整个农场规模的群落结构和功能。来自10对有机农场和传统农场复制品的定量食物网表明，有机农场在三个营养级（植物、食草动物和寄生蜂）上的物种显著更多，且网络结构显著不同。有机农场的食草动物受到有机农场寄生蜂物种的攻击比传统农场更多。然而，网络结构的差异并未转化为对模拟物种丧失的稳健性差异，并且我们发现在各种寄主物种中寄生率（自然害虫控制）没有差异。此外，一项操纵性田间实验表明，有机农场寄生蜂较高的物种丰富度并未增加用于生物测定生态系统服务的新型食草动物的死亡率。这些差异的解释可能包括两种耕作系统在管理策略和景观结构上的固有差异。
