Data from: Unravelling the role of allochthonous aquatic resources to food web structure in a tropical riparian forest

1. The role of matter and energy flow across ecosystem boundaries for subsidized consumer populations is well known. However, little is known on the effects of allochthonous subsidies on food web structure and trophic niche dimensions of consumers in the tropics. 2. We excluded allochthonous aquatic insects from tropical streams using greenhouse-type exclosures to test the influence of aquatic allochthonous subsidies on the trophic structure and niche dimensions of terrestrial predators using stable isotope methods. 3. In exclosure treatments, abundance and biomass of terrestrial predators, and biomass of phytophages, decreased and increased, respectively. Vegetation-living predators were more responsive to allochthonous inputs than those living on the ground. Overall, lower availability of allochthonous inputs did not affect community-wide metrics and niche width of predators. However, the niche width of some spider families had very low overlap between treatments, and others had wider isotopic niches in the control than exclusion treatment. Most of the C and N in predators living in control stretches came from aquatic subsidies, and those predators living in exclusion treatments switched their diets to terrestrial sources, showing a preference of predators for allochthonous subsidies. 4. Our results suggest that allochthonous subsidies are also relevant to tropical fauna living upon vegetation. Moreover, allochthonous resources may amplify the niche dimension of certain predators, or considerably change the trophic niche of others. Our study highlights the importance of including modern isotopic tools in elucidating the role of allochthonous resources on the patterns of trophic structure and niche dimensions of consumers from donor ecosystems.1. 物质与能量跨生态系统边界流动，对依赖外源性营养补贴（allochthonous subsidies）的消费者种群的作用已得到广泛阐明。然而，目前学界对热带生态系统中，外源性营养补贴如何影响食物网结构以及消费者的营养生态位维度，仍缺乏足够认知。 2. 我们采用温室型围隔装置（greenhouse-type exclosures），将异源水生昆虫隔绝于热带溪流之外以开展控制实验，并借助稳定同位素法（stable isotope methods），探究水生外源性营养补贴对陆生捕食者的营养结构及其生态位维度的影响。 3. 围隔处理组中，陆生捕食者的丰度与生物量均下降，植食性动物（phytophages）的生物量则上升。栖息于植被层的捕食者，其对异源输入的响应敏感度显著高于地面栖息的同类。整体而言，异源输入可用性的降低并未对捕食者的群落水平指标（community-wide metrics）及生态位宽度产生显著影响。然而，部分蜘蛛科类群的同位素生态位（isotopic niches）在不同处理组间的重叠度极低，其余类群在对照组中的同位素生态位宽度显著高于围隔处理组。对照组溪流样点中的陆生捕食者，其体内绝大多数碳与氮元素均来自水生外源性补贴；而围隔处理组的捕食者则将饮食来源切换至陆生资源，体现出其对外源性营养补贴的偏好性。 4. 本研究结果表明，外源性营养补贴对栖息于植被层的热带动物类群同样具有重要意义。此外，外源性资源或可扩大部分捕食者的生态位维度，或显著改变其余类群的营养生态位。本研究强调，需将现代同位素分析工具纳入研究范畴，以阐明外源性资源在供体生态系统消费者的营养结构模式与生态位维度形成过程中的作用。