Hopper Garrett W, Gido Keith B, Vaughn Caryn C, Parr Thomas B, Popejoy Traci G, Atkinson Carla L, Gates Kiza K
Division of Biology, Kansas State University, 116 Ackert Hall, Manhattan, KS, 66506, USA.
Oklahoma Biological Survey and Department of Biology, University of Oklahoma, Norman, OK, USA.
Oecologia. 2018 Dec;188(4):1133-1144. doi: 10.1007/s00442-018-4277-1. Epub 2018 Oct 20.
Animals can play important roles in cycling nutrients [hereafter consumer-driven nutrient dynamics (CND)], but researchers typically simplify animal communities inhabiting dynamic environments into single groups that are tested under relatively static conditions. We propose a conceptual framework and present empirical evidence for CND that considers the potential effects of spatially overlapping animal groups within dynamic ecosystems. Because streams can maintain high biomass of mussels and fish, we were able to evaluate this framework by testing if biogeochemical hotspots generated by stable aggregations of mussels attract fishes. We predicted that spatial overlap between these groups may increase the flux of mineralized nutrients. We quantified how different fish assemblage biomass was between mussel bed reaches and reaches without mussels. We compared fish and mussel biomass at mussel beds to test whether differences in animal biomass mediate their contributions to nutrient cycling through nitrogen and phosphorous excretion. We estimated areal excretion rates for each group by combining biomass estimates with measured excretion rates. Fish biomass was homogeneously distributed, except following a period of low flow when fish were more concentrated at mussel beds. Mussel biomass was consistently an order of magnitude greater than fish biomass and mussel areal excretion rates exceeded fish excretion rates. However, the magnitude of those differences varied spatially and temporally. Mussel excretion stoichiometry varied with changes in assemblage composition, while fish excretion stoichiometry varied little. Biogeochemical hotspots associated with mussels did not generally overlap with fish aggregations, thus, under these conditions, animal processes appear to exert additive ecosystem effects.
动物在养分循环中可发挥重要作用（以下简称消费者驱动的养分动态，CND），但研究人员通常会将栖息于动态环境中的动物群落简化为单一群体，并在相对静态的条件下进行测试。我们提出了一个概念框架，并给出了CND的实证证据，该框架考虑了动态生态系统中空间重叠的动物群体的潜在影响。由于溪流能够维持贻贝和鱼类的高生物量，我们得以通过测试贻贝稳定聚集产生的生物地球化学热点是否吸引鱼类来评估这一框架。我们预测这些群体之间的空间重叠可能会增加矿化养分的通量。我们量化了贻贝床河段和无贻贝河段之间不同鱼类组合生物量的差异。我们比较了贻贝床处的鱼类和贻贝生物量，以测试动物生物量的差异是否通过氮和磷的排泄介导它们对养分循环的贡献。我们通过将生物量估计值与实测排泄率相结合来估算每个群体的单位面积排泄率。鱼类生物量分布均匀，只是在一段低流量期后，鱼类在贻贝床处更为集中。贻贝生物量始终比鱼类生物量高一个数量级，且贻贝的单位面积排泄率超过鱼类排泄率。然而，这些差异的幅度在空间和时间上有所变化。贻贝排泄化学计量随组合组成的变化而变化，而鱼类排泄化学计量变化不大。与贻贝相关的生物地球化学热点通常与鱼类聚集区不重叠，因此，在这些条件下，动物过程似乎对生态系统产生累加效应。
