Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 47, NL-6700 AA Wageningen, The Netherlands.
Ecol Appl. 2012 Jan;22(1):229-39. doi: 10.1890/11-0941.1.
Lake Victoria in East Africa is the world's second largest freshwater system. Over the past century the ecosystem has undergone drastic changes. Some 30 years after the introduction of Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus) in the 1950s, the highly diverse community of native haplochromines collapsed, leaving a system dominated by only four species: the native cyprinid dagaa (Rastrineobola argentea) and shrimp (Caridina nilotica), as well as the introduced Nile perch and Nile tilapia. More recently, an unexpected resurgence of haplochromines has been reported. To understand these changes in terms of ecosystem functioning and of changes in growth of trophic groups, we created mass balances of the food web near Mwanza, Tanzania, before, during, and after the Nile perch boom (1977, 1987, and 2005), using the application ECOPATH. We connected these mass balances with a dynamic model assuming linear trends in net growth rates of the trophic groups. Our analysis suggests that the Nile perch boom initially altered the biomass distribution over trophic levels. Also, results indicate that not only fishing but also changes at the detritivores' trophic level might have played an important role in driving changes in the system. Both the mass balances and the dynamic model connecting them reveal that, after a major distortion during the Nile perch boom, the biomass distribution over the main trophic levels had largely recovered its original (1977) state by 2005. However, no such return appeared in terms of community structure. Biodiversity in the new state is dramatically lower, consisting of introduced species and a few native surviving species. We conclude that at an aggregate level Lake Victoria's ecosystem has proved to be resilient in the sense that its overall trophic structure has apparently recovered after a major perturbation. By contrast, its intricate functional structure and associated biodiversity have proved to be fragile and seem unlikely to recover.
非洲东部的维多利亚湖是世界上第二大淡水系统。在过去的一个世纪里，该生态系统发生了巨大的变化。在 20 世纪 50 年代引入尼罗河鲈鱼（Lates niloticus）和尼罗河罗非鱼（Oreochromis niloticus）大约 30 年后，高度多样化的本地haplochromines 群落崩溃了，只剩下四个物种：本地鲤科 dagaa（Rastrineobola argentea）和虾（Caridina nilotica），以及引入的尼罗河鲈鱼和尼罗河罗非鱼。最近，有人报告说，haplochromines 出乎意料地大量繁殖。为了从生态系统功能和营养群体生长变化的角度来理解这些变化，我们在坦桑尼亚姆万扎附近创建了食物网的质量平衡，在尼罗河鲈鱼繁荣之前（1977 年）、期间（1987 年）和之后（2005 年），使用 ECOPATH 应用程序。我们将这些质量平衡与一个动态模型连接起来，该模型假设营养群体的净增长率呈线性趋势。我们的分析表明，尼罗河鲈鱼的繁荣最初改变了营养水平的生物量分布。此外，结果表明，不仅是捕鱼，而且碎屑食者营养级别的变化可能在推动系统变化方面发挥了重要作用。质量平衡和连接它们的动态模型都表明，在尼罗河鲈鱼繁荣期间发生了重大扭曲之后，到 2005 年，主要营养水平的生物量分布已经基本恢复到原来的（1977 年）状态。然而，在群落结构方面，并没有出现这种回归。新状态下的生物多样性大大降低，由引入的物种和少数幸存的本地物种组成。我们的结论是，从总体水平上看，维多利亚湖的生态系统具有弹性，因为在受到重大干扰后，其整体营养结构显然已经恢复。相比之下，它复杂的功能结构和相关的生物多样性已经被证明是脆弱的，似乎不太可能恢复。
