Role of the fish Astyanax aeneus (Characidae) as a keystone nutrient recycler in low-nutrient neotropical streams.
Role of the fish Astyanax aeneus (Characidae) as a keystone nutrient recycler in low-nutrient neotropical streams.
复制标题
Astyanax aeneus（Characidae）鱼作为低营养新热带溪流中关键营养物回收者的作用。
作者：
G. Small;C. Pringle;M. Pyron;J. Duff
在陆地和水生生态系统中，动物的营养循环是一个潜在的重要的生物地球化学过程。个别物种的化学计量特征可能导致某些类群在养分循环中扮演着与其生物量不成比例的重要角色，扮演着关键的营养循环者的角色。我们研究了控制12种新热带鱼类在四条河流中营养循环的相对贡献的因素，这些河流跨越了一系列磷(P)水平。在高磷条件下(135微克/L可溶性活性磷)，大多数物种摄食富磷饲料，跨物种的排磷率较高。在低磷条件下(3微克/L SRP)，水生食物资源中的磷被耗尽，体内磷含量较高的物种表现出低的磷循环利用率。然而，由陆地输入补贴的鱼类与水生磷的供应脱钩，因此以不成比例的高比率排出磷。其中一种，Astianax aeneus(Characidae)，占本研究重点低磷研究溪流鱼类种群总数的12%和总生物量的18%，但其磷排泄率是其他丰富鱼类的10倍。因此，我们估计非洲按蚊排出的磷占该鱼群循环利用的磷的90%，也提供了这个磷有限的生态系统中约90%的溪流磷需求。氮素排泄率在物种间差异不大，特定物种对生态系统氮循环的贡献在很大程度上取决于该物种的总生物量。由于不同鱼类的磷排泄率差异很大，生态系统水平的磷循环可能对磷限制系统中鱼类群落结构的变化特别敏感。
Nutrient recycling by animals is a potentially important biogeochemical process in both terrestrial and aquatic ecosystems. Stoichiometric traits of individual species may result in some taxa playing disproportionately important roles in the recycling of nutrients relative to their biomass, acting as keystone nutrient recyclers. We examined factors controlling the relative contribution of 12 Neotropical fish species to nutrient recycling in four streams spanning a range of phosphorus (P) levels. In high-P conditions (135 microg/L soluble reactive phosphorus, SRP), most species fed on P-enriched diets and P excretion rates were high across species. In low-P conditions (3 microg/L SRP), aquatic food resources were depleted in P, and species with higher body P content showed low rates of P recycling. However, fishes that were subsidized by terrestrial inputs were decoupled from aquatic P availability and therefore excreted P at disproportionately high rates. One of these species, Astyanax aeneus (Characidae), represented 12% of the total population and 18% of the total biomass of the fish assemblage in our focal low-P study stream but had P excretion rates > 10-fold higher than other abundant fishes. As a result, we estimated that P excretion by A. aeneus accounted for 90% of the P recycled by this fish assemblage and also supplied approximately 90% of the stream P demand in this P-limited ecosystem. Nitrogen excretion rates showed little variation among species, and the contribution of a given species to ecosystem N recycling was largely dependent upon the total biomass of that species. Because of the high variability in P excretion rates among fish species, ecosystem-level P recycling could be particularly sensitive to changes in fish community structure in P-limited systems.