Effects of the introduction of an omnivorous fish on the biodiversity and functioning of an upland Amazonian lake

ABSTRACT The introduction of nonnative species is one of the main threats to freshwater ecosystems. Although omnivory and intraguild predation are common in those systems, little is known about the effects of introduced omnivorous fish on pelagic and littoral communities. This study tested predictions of food-web theory regarding the effects of omnivorous fish introduction on previously fishless lakes in the Amazonian uplands of Serra dos Carajás, Pará, Brazil. The trophic structure of two similar lakes, one with and the other without the introduced omnivorous fish Astyanax bimaculatus, was compared using a data series of biotic variables collected from both lakes twice a year from 2010 to 2013. Zooplankton was more abundant in the lake with fish, and the zooplankton composition differed between lakes. Phytoplankton richness and chlorophyll-a were higher in the lake with the introduced fish than in the fishless lake regardless of phosphorus limitation. For the benthic macroinvertebrate communities, species richness and biomass were higher in the fishless lake. Our results also indicate that A. bimaculatus has the potential to link pelagic and littoral habitats through nutrient cycling. The differences observed between the studied lakes are consistent with predictions from food-web theory regarding the effects of multichain omnivorous fish on trophic dynamics. Despite limitations regarding replication at the ecosystem level, it is possible to infer from our findings that the introduction of an omnivorous fish might have changed lake overall functioning.

摘要：非本土物种的引入是淡水生态系统面临的主要威胁之一。尽管杂食性与集团内捕食（intraguild predation）在这类生态系统中极为普遍，但学界对引入的杂食性鱼类对浮游与沿岸群落的影响仍知之甚少。本研究针对巴西帕拉州卡拉加斯山脉（Serra dos Carajás）亚马逊高地内此前无鱼类栖息的湖泊，检验了食物网理论关于杂食性鱼类引入效应的预测。研究选取两座特征相似的湖泊，一座引入了杂食性鱼类双斑丽脂鲤（Astyanax bimaculatus），另一座未引入该物种；通过2010年至2013年每年两次采集的两座湖泊的生物变量数据集，对比二者的营养结构差异。结果显示，有鱼湖泊中的浮游动物丰度更高，且两座湖泊的浮游动物群落组成存在显著差异；无论磷限制条件如何，引入鱼类的湖泊中浮游植物物种丰富度与叶绿素a（chlorophyll-a）浓度均高于无鱼湖泊；而底栖大型无脊椎动物群落的物种丰富度与生物量则在无鱼湖泊中更高。本研究还发现，双斑丽脂鲤有可能通过营养循环连接浮游与沿岸生境。观测到的两座湖泊间的差异与食物网理论关于多链杂食性鱼类对营养动态影响的预测一致。尽管在生态系统尺度上的重复样本存在局限性，但从研究结果仍可推断：引入杂食性鱼类可能会改变湖泊整体的生态系统功能。