Aggregated filter-feeding consumers alter nutrient limitation: consequences for ecosystem and community dynamics
Aggregated filter-feeding consumers alter nutrient limitation: consequences for ecosystem and community dynamics
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DOI：
10.1890/12-1531.1
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发表时间：
2013-06-01
期刊：
影响因子：
4.8
通讯作者：
Cooper, Joshua T.
中科院分区：
文献类型：
--
作者：
Atkinson, Carla L.;Vaughn, Caryn C.;Cooper, Joshua T.
养分循环是生态系统中联系生物的关键过程。这在河流环境中尤其明显，因为在河流环境中，营养物质很容易被吸收，并在下游的轨迹中通过系统循环。生态化学计量学预测，不同元素的生物地球化学循环是相互依赖的，因为驱动这些循环的生物体需要固定比例的营养物质。越来越多的人认识到动物在整个生态系统的生物地球化学循环中起着重要作用。特别是，消费者的密集聚集可以通过营养转运在水生生态系统中产生生物地球化学热点。我们预测滤食性淡水贻贝，作为物种，高生物量的聚集体，将通过改变营养限制和藻类动态，在溪流中产生生物地球化学热点。在一项野外研究中，我们在贻贝丰度高和低的地区使用营养物扩散基质来控制氮和磷，记录藻类生长和群落组成，并在三条河流（Kiamichi、Little和Mountain Fork river，美国中南部）的18个地点测定贻贝排泄化学计量。我们的研究结果表明，贻贝通过改变限制初级生产力的营养物质，极大地影响了生态系统过程。无贻贝的生境受氮限制，固氮蓝藻相对丰度高26%，而贻贝密度高的生境受氮磷限制，以硅藻为主。这些结果证实了我们的排泄实验的结果；通径分析表明，贻贝排泄物对河流水体N: P的影响较大。由于贻贝排泄物的高N: P，严格的N限制被缓解，系统转变为N和P的共同限制。这表明贻贝聚集的营养物质转运对这些河流的营养动态和藻类物种组成很重要。我们的研究强调了消费者和这一濒危动物群对水生生态系统中营养循环和群落动态的重要性。
Nutrient cycling is a key process linking organisms in ecosystems. This is especially apparent in stream environments in which nutrients are taken up readily and cycled through the system in a downstream trajectory. Ecological stoichiometry predicts that biogeochemical cycles of different elements are interdependent because the organisms that drive these cycles require fixed ratios of nutrients. There is growing recognition that animals play an important role in biogeochemical cycling across ecosystems. In particular, dense aggregations of consumers can create biogeochemical hotspots in aquatic ecosystems via nutrient translocation. We predicted that filter-feeding freshwater mussels, which occur as speciose, high-biomass aggregates, would create biogeochemical hotspots in streams by altering nutrient limitation and algal dynamics. In a field study, we manipulated nitrogen and phosphorus using nutrient-diffusing substrates in areas with high and low mussel abundance, recorded algal growth and community composition, and determined in situ mussel excretion stoichiometry at 18 sites in three rivers (Kiamichi, Little, and Mountain Fork Rivers, south-central United States). Our results indicate that mussels greatly influence ecosystem processes by modifying the nutrients that limit primary productivity. Sites without mussels were N-limited with similar to 26% higher relative abundances of N-fixing blue-green algae, while sites with high mussel densities were co-limited (N and P) and dominated by diatoms. These results corroborated the results of our excretion experiments; our path analysis indicated that mussel excretion has a strong influence on stream water column N: P. Due to the high N: P of mussel excretion, strict N-limitation was alleviated, and the system switched to being co-limited by both N and P. This shows that translocation of nutrients by mussel aggregations is important to nutrient dynamics and algal species composition in these rivers. Our study highlights the importance of consumers and this imperiled faunal group on nutrient cycling and community dynamics in aquatic ecosystems.