Data from: Dietary changes in predators and scavengers in a nocturnally illuminated riparian ecosystem

Aquatic and terrestrial ecosystems are linked by fluxes of carbon and nutrients in riparian areas. Processes that alter these fluxes may therefore change the diet and composition of consumer communities. We used stable carbon isotope (δ13C) analyses to test whether the increased abundance of aquatic prey observed in another study led to a dietary shift in riparian consumers in areas illuminated by artificial light at night (ALAN). We measured the contribution of aquatic-derived carbon to diets in riparian arthropods in experimentally lit and unlit sites along an agricultural drainage ditch in northern Germany. The δ13C signature of the spider Pachygnatha clercki (Tetragnathidae) was 0.7‰ lower in the ALAN-illuminated site in summer, indicating a greater assimilation of aquatic prey. Bayesian mixing models also supported higher intake of aquatic prey under ALAN in summer (34% versus 21%). In contrast, isotopic signatures for P. clercki (0.3‰) and Pardosa prativaga (0.7‰) indicated a preference for terrestrial prey in the illuminated site in summer. Terrestrial prey intake increased in spring for P. clerckii under ALAN (from 70% to 74%) and in spring and autumn for P. prativaga (from 68% to 77% and from 67% to 72%) and Opiliones (from 68% to 72%; 68% to 75%). This was despite most of the available prey (up to 80%) being aquatic in origin. We conclude that ALAN changed the diet of riparian secondary consumers by increasing the density of both aquatic and terrestrial prey. Dietary changes were species- and season-specific, indicating that the effects of ALAN may interact with phenology and feeding strategy. Because streetlights can occur in high density near freshwaters, ALAN may have widespread effects on aquatic-terrestrial ecosystem linkages.

河岸带（riparian areas）的碳与营养盐通量将水生与陆地生态系统联结为整体。因此，能够改变这类通量的过程，可改变消费者群落的食性与组成结构。本研究采用稳定碳同位素(δ¹³C)分析方法，旨在验证已有研究中观测到的水生猎物丰度提升现象，是否会导致夜间人工光照（artificial light at night, ALAN）环境下河岸带消费者的食性发生转变。我们于德国北部一处农业排水沟沿线的实验光照与无光照样点中，测定了河岸带节肢动物日粮中水生来源碳的占比。夏季时，ALAN光照样点内蜘蛛Pachygnatha clercki（长脚蛛科Tetragnathidae）的δ¹³C信号值较对照组低0.7‰，表明其对水生猎物的同化程度更高。贝叶斯混合模型(Bayesian mixing models)的结果也证实，夏季ALAN环境下水生猎物的摄入占比更高（34% vs 21%）。与之相反，夏季光照样点内P. clercki（δ¹³C信号差值0.3‰）与Pardosa prativaga（δ¹³C信号差值0.7‰）的同位素信号显示，二者更偏好取食陆地猎物。春季时，ALAN环境下P. clerckii的陆地猎物摄入占比从70%提升至74%；P. prativaga与盲蛛目(Opiliones)的陆地猎物摄入占比则在春季与秋季均有所提升：前者从68%升至77%、67%升至72%，后者从68%升至72%、68%升至75%。尽管研究区域内绝大多数可获取猎物（最高可达80%）的来源为水生，上述现象仍会发生。本研究结论表明，ALAN通过提升水生与陆地猎物的种群密度，改变了河岸带次级消费者的食性。食性转变呈现物种特异性与季节特异性，提示ALAN的生态效应可能与物候及取食策略存在交互作用。由于淡水生境周边的路灯布设密度通常较高，ALAN可能对水生-陆地生态系统的联结产生广泛影响。