Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106;
Marine Science Institute, University of California, Santa Barbara, CA 93106.
Proc Natl Acad Sci U S A. 2018 May 29;115(22):E5028-E5037. doi: 10.1073/pnas.1800407115. Epub 2018 May 14.
Cross-boundary transfers of nutrients can profoundly shape the ecology of recipient systems. The common hippopotamus, , is a significant vector of such subsidies from terrestrial to river ecosystems. We compared river pools with high and low densities of to determine how subsidies shape the chemistry and ecology of aquatic communities. Our study watershed, like many in sub-Saharan Africa, has been severely impacted by anthropogenic water abstraction reducing dry-season flow to zero. We conducted observations for multiple years over wet and dry seasons to identify how hydrological variability influences the impacts of During the wet season, when the river was flowing, we detected no differences in water chemistry and nutrient parameters between pools with high and low densities of Likewise, the diversity and abundance of fish and aquatic insect communities were indistinguishable. During the dry season, however, high-density s pools differed drastically in almost all measured attributes of water chemistry and exhibited depressed fish and insect diversity and fish abundance compared with low-density pools. Scaled up to the entire watershed, we estimate that in this hydrologically altered watershed reduces dry-season fish abundance and indices of gamma-level diversity by 41% and 16%, respectively, but appears to promote aquatic invertebrate diversity. Widespread human-driven shifts in hydrology appear to redefine the role of , altering their influence on ecosystem diversity and functioning in a fashion that may be more severe than presently appreciated.
营养物质的跨界转移可以深刻地塑造受体系统的生态。普通河马（Hippopotamus amphibius）就是这种从陆地向河流生态系统输送养分的重要载体。我们比较了河马密度高和低的河潭，以确定河马的这种养分输送如何塑造水生群落的化学和生态。与撒哈拉以南非洲的许多流域一样，我们的研究流域受到了人为抽取水资源的严重影响，导致旱季流量降至零。我们进行了多年的干湿季观测，以确定水文变化如何影响河马的影响。在雨季，当河水流动时，我们没有发现河马密度高和低的河潭之间在水质和养分参数上有差异。同样，鱼类和水生昆虫群落的多样性和丰度也无法区分。然而，在旱季，河马密度高的河潭在水质的几乎所有测量属性上都有明显差异，与河马密度低的河潭相比，鱼类和昆虫的多样性以及鱼类的丰度明显降低。扩展到整个流域，我们估计在这个水文发生变化的流域，河马的数量减少了 41%，γ级多样性指数减少了 16%，但似乎促进了水生无脊椎动物的多样性。广泛的人为驱动的水文变化似乎重新定义了河马的作用，改变了它们对生态系统多样性和功能的影响，这种影响可能比目前人们所认识到的更为严重。
