Ecological networks can provide insight into how biodiversity loss and changes in species interactions impact the delivery of ecosystem services. In agroecosystems that vary in management practices, quantifying changes in ecological network structure across gradients of local and landscape composition can inform both the ecology and function of productive agroecosystems. In this study, we examined natural‐enemy–herbivore co‐occurrence networks associated with Brassica oleracea (cole crops), a common crop in urban agricultural systems. Specifically, we investigated how local management characteristics of urban community gardens and the landscape composition around them affect (1) the abundance of B. oleracea herbivores and their natural enemies, (2) the natural‐enemy : herbivore ratio, and (3) natural‐enemy–herbivore co‐occurrence network metrics. We sampled herbivores and natural enemies in B. oleracea plants in 24 vegetable gardens in the California, USA central coast region. We also collected information on garden characteristics and land‐use cover of the surrounding landscape (2 km radius). We found that increased floral richness and B. oleracea abundance were associated with increased parasitoid abundance, non‐aphid herbivore abundance, and increased network vulnerability; increased vegetation complexity suppressed parasitoid abundance, but still boosted network vulnerability. High agricultural land‐use cover in the landscape surrounding urban gardens was associated with lower predator, parasitoid, and non‐aphid herbivore abundance, lower natural‐enemy : herbivore ratios, lower interaction richness, and higher trophic complementarity. While we did not directly measure pest control, higher interaction richness, higher vulnerability, and lower trophic complementarity are associated with higher pest control services in other agroecosystems. Thus, if gardens function similarly to other agroecosystems, our results indicate that increasing vegetation complexity, including trees, shrubs, and plant richness, especially within gardens located in intensively farmed landscapes, could potentially enhance the biodiversity and abundance of natural enemies, supporting ecological networks associated with higher pest control services.

中文翻译：

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沿城市农业生态系统的局部管理和景观梯度分布的天然敌草食人动物网络。

生态网络可以提供有关生物多样性丧失和物种相互作用变化如何影响生态系统服务提供的见解。在管理方式各异的农业生态系统中，量化局部和景观组成梯度上的生态网络结构变化，可以为生产型农业生态系统的生态和功能提供依据。在这项研究中，我们研究了与甘蓝型油菜（油菜作物）（城市农业系统中的常见作物）相关的天然-敌食-草食动物共现网络。具体而言，我们调查了城市社区花园的当地管理特征及其周围的景观组成如何影响（1）油菜花的丰富度草食动物及其天敌，（2）天敌：草食动物比率，以及（3）天敌-草食动物共现网络指标。我们在美国加利福尼亚州中部沿海地区的24个菜园中对油菜芽孢杆菌植物中的草食动物和天敌进行了采样。我们还收集了有关花园特征和周围景观（半径2公里）的土地利用覆盖范围的信息。我们发现增加了花的丰富度和B. oleracea丰度与寄生虫的丰度增加，非蚜虫草食动物的丰度增加以及网络脆弱性增加有关；植被复杂性的增加抑制了类寄生物的丰度，但仍然加剧了网络的脆弱性。城市花园周围景观的农业土地利用覆盖率较高，这与较低的食肉动物，寄生虫和非蚜虫草食动物的丰度，较低的天敌：草食动物比率，较低的相互作用丰富度和较高的营养互补性有关。尽管我们没有直接衡量害虫控制，但更高的互动度，更高的脆弱性和更低的营养互补性与其他农业生态系统中更高的害虫控制服务相关。因此，如果花园的功能类似于其他农业生态系统，那么我们的结果表明，植被的复杂性不断增加，包括树木，灌木，