Data from: The effects of pastoral intensification on the feeding interactions of generalist predators in streams

Land use change can alter trophic interactions with wide-ranging functional consequences, yet the consequences for aquatic food webs have been little-studied. In part, this may reflect the challenges of resolving the diets of aquatic organisms using classical gut contents analysis, especially for soft-bodied prey. We used next generation sequencing to resolve prey use in nearly 400 individuals of two predatory invertebrates (the Caddisfly, Rhyacophila dorsalis, and the Stonefly Dinocras cephalotes) in streams draining land with increasingly intensive livestock farming. Rhyacophila dorsalis occurred in all streams, whereas D. cephalotes was restricted to low intensities, allowing us to test whether: i) apparent sensitivity to agriculture in the latter species reflects a more specialised diet and ii) diet in R. dorsalis varied between sites with and without D. cephalotes. DNA was extracted from dissected gut contents, amplified without blocking probes and sequenced using Ion Torrent technology. Both predators were generalists, consuming 30 prey taxa with preference for taxa that were abundant in all streams or that increased with intensification. Where both predators were present, their diets were nearly-identical, and R. dorsalis’s diet was virtually unchanged in the absence of D. cephalotes. The loss of D. cephalotes from more intensive sites was probably due to physicochemical stressors, such as sedimentation, rather than to dietary specialization, although wider biotic factors (e.g. competition with other predatory taxa) could not be excluded. This study provides a uniquely detailed description of predator diets along a land use intensity gradient, offering new insights into how anthropogenic stressors affect stream communities.土地利用变化可改变营养相互作用并带来广泛的功能性后果，但目前针对水生食物网的相关影响研究仍较为匮乏。这在一定程度上或许源于传统肠道内容物分析技术在解析水生生物食性时存在局限，针对软体猎物的分析尤为困难。本研究借助下一代测序技术，对流经畜禽养殖强度逐步增强的流域的溪流中的两类捕食性无脊椎动物——石蛾（Caddisfly）*Rhyacophila dorsalis* 与石蝇（Stonefly）*Dinocras cephalotes* 的近400个个体进行了食性解析。*Rhyacophila dorsalis* 在所有采样溪流中均有分布，而*Dinocras cephalotes* 仅局限于养殖强度较低的区域，借此我们得以验证两个研究假说：① 后者对农业活动的表观敏感性是否源于其更为特化的食性；② *Rhyacophila dorsalis* 的食性在是否共存有*Dinocras cephalotes* 的样地间是否存在差异。研究人员从解剖获取的肠道内容物中提取DNA，未使用封闭探针进行扩增，随后通过Ion Torrent测序技术完成测序。两类捕食者均为泛食性物种，共取食30个猎物分类单元，且偏好于在所有溪流中种群丰度较高，或随养殖强度提升而数量增加的猎物类群。在两类捕食者共存的样地中，二者的食性几乎完全一致；而在无*Dinocras cephalotes* 分布的样地中，*Rhyacophila dorsalis* 的食性几乎未发生改变。在养殖强度更高的样地中，*Dinocras cephalotes* 的消失大概率源于理化胁迫因子（如沉积物淤积）而非食性特化，但仍无法排除更广泛的生物因子（例如与其他捕食类群的竞争）的影响。本研究沿着土地利用强度梯度，对捕食者食性进行了前所未有的详尽描述，为解析人为胁迫如何影响溪流群落提供了全新的研究视角。