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级互作（trophic interactions）并产生广泛的功能效应，但目前针对水生食物网（aquatic food webs）的此类效应研究仍较为匮乏。这在一定程度上可归因于：采用传统肠道内含物分析方法解析水生生物食性存在诸多挑战，针对软体猎物的分析难度尤甚。我们借助下一代测序（next generation sequencing）技术，对源自畜禽养殖强度不断升高的流域溪流中的两种捕食性无脊椎动物——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*仅存在于畜禽养殖强度较低的样点中，借此我们得以验证两个假说：其一，该石蝇物种对农业活动的表观敏感性是否源于其特化的食性；其二，*Rhyacophila dorsalis*的食性在有无*Dinocras cephalotes*共存的样点间是否存在差异。研究人员从解剖得到的肠道内含物中提取DNA，在不使用封闭探针的条件下进行扩增，并借助Ion Torrent测序技术（Ion Torrent）完成了测序。两种捕食者均为泛食性类群，共取食30个猎物类群，且对两类猎物存在取食偏好：一类是在所有溪流中丰度较高的类群，另一类是随畜禽养殖强度升高而丰度上升的类群。当两种捕食者共存时，二者的食性几乎完全一致；而在无*Dinocras cephalotes*存在的样点中，*Rhyacophila dorsalis*的食性几乎未发生改变。尽管无法排除与其他捕食类群竞争等更广范围的生物因子影响，但高养殖强度样点中*Dinocras cephalotes*的消失大概率是由沉积物淤积等物理化学胁迫因素导致，而非其食性特化所致。本研究沿土地利用强度梯度为捕食者食性提供了前所未有的详尽描述，为解析人为胁迫因子如何影响溪流群落提供了全新视角。