Kautza Adam, Mazeika S, Sullivan P
Ecology. 2016 Mar;97(3):694-705.
Rivers are increasingly recognized as providing nutritional subsidies (i.e., energy and nutrients) to adjacent terrestrial food webs via depredation of aquatic organisms (e.g., emergent aquatic insects, crayfish, fish) by terrestrial consumers. However, because these prey organisms assimilate energy from both aquatic (e.g., benthic algae, phytoplankton, aquatic macrophytes) and terrestrial (e.g., riparian leaf detritus) primary producers, river subsidies to terrestrial consumers represent a combination of aquatically and terrestrially derived energy. To date, the explicit contribution of energy derived from aquatic primary producers to terrestrial consumers has not been fully explored yet might be expected to be quantitatively important to terrestrial food webs. At 12 reaches along a 185-km segment of the sixth-order Scioto River system (Ohio, USA), we quantified the relative contribution of energy derived from aquatic primary producers to a suite of terrestrial riparian consumers that integrate the adjacent landscape across multiple spatial scales through their foraging activities (tetragnathid spiders, rove beetles, adult coenagrionid damselflies, riparian swallows, and raccoons). We used naturally abundant stable isotopes (13C and 15N) of periphyton, phytoplankton, macrophytes, and terrestrial vegetation to evaluate the energetic contribution of aquatic primary producers to terrestrial food webs. Shoreline tetragnathid spiders were most reliant on aquatic primary producers (50%), followed by wider-ranging raccoons (48%), damselflies (44%), and riparian swallows (41%). Of the primary producers, phytoplankton (19%) provisioned the greatest nutritional contribution to terrestrial consumers (considered collectively), followed by periphyton (14%) and macrophytes (11%). Our findings provide empirical evidence that aquatic primary producers of large streams and rivers can be a critical nutritional resource for terrestrial food webs. We also show that aquatically derived nutrition contributes to both shoreline and broader-ranging terrestrial consumers and thus may be an important landscape-scale energetic linkage between rivers and upland habitats.
河流越来越被认为通过陆地消费者捕食水生生物（如羽化的水生昆虫、小龙虾、鱼类）为相邻的陆地食物网提供营养补贴（即能量和营养物质）。然而，由于这些猎物生物从水生（如底栖藻类、浮游植物、水生大型植物）和陆地（如河岸落叶碎屑）初级生产者那里同化能量，河流对陆地消费者的补贴代表了水生和陆地来源能量的组合。迄今为止，来自水生初级生产者的能量对陆地消费者的明确贡献尚未得到充分探索，但可能预计对陆地食物网在数量上具有重要意义。在美国俄亥俄州第六级斯科托河水系185公里河段的12个河段，我们量化了来自水生初级生产者的能量对一系列陆地河岸消费者的相对贡献，这些消费者通过其觅食活动在多个空间尺度上整合相邻景观（长脚蛛、隐翅虫、成年豆娘、河岸燕子和浣熊）。我们利用附生植物、浮游植物、大型植物和陆地植被中天然丰富的稳定同位素（碳-13和氮-15）来评估水生初级生产者对陆地食物网的能量贡献。河岸长脚蛛最依赖水生初级生产者（50%），其次是活动范围更广的浣熊（48%）、豆娘（44%）和河岸燕子（41%）。在初级生产者中，浮游植物（19%）对陆地消费者（总体而言）提供了最大的营养贡献，其次是附生植物（14%）和大型植物（立1%）。我们的研究结果提供了实证证据，表明大型溪流和河流的水生初级生产者可能是陆地食物网的关键营养资源。我们还表明，来自水生的营养物质对河岸和活动范围更广的陆地消费者都有贡献，因此可能是河流与高地栖息地之间重要的景观尺度能量联系。
