Shallow lakes can change states in response to manipulations of top predators. In most reported experiments, the top piscivore has been a fish. However, low-latitude lakes typically support non-piscine piscivores, including mammals, birds, and reptiles. The roles of these groups have been little investigated, and whether they are more important as piscivores than fish remains unknown. We report both a longitudinal (2001–2018) and a cross-sectional (2012) study of the bird, caiman, and giant otter populations of floodplain lakes in Perú’s Manu National Park. We compare the three groups, after removing the effects of taxonomic status and body mass, using allometric equations to estimate the field metabolic rate (FMR) for each group in each lake. Giant otters emerge as the dominant piscivore in lakes that support a resident family, with an energy requirement more than twice that of piscivorous birds and more than seven times that of caiman. However, giant otters were resident in only eight of 27 surveyed lakes. Indirect evidence suggests that these eight lakes are more productive than lakes not occupied by otters. The fact that lakes occupied by otters are dominated by phytoplankton suggests an underlying five-tiered trophic structure in keeping with the prominence of alternating levels in the structure of food webs.

中文翻译：

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亚马逊河上游泛滥平原湖泊中的移动食鱼动物和自上而下强迫的性质

浅湖可以响应顶级捕食者的操纵而改变状态。在大多数报道的实验中，最常见的食鱼动物是鱼。然而，低纬度湖泊通常支持非鱼类食鱼动物，包括哺乳动物、鸟类和爬行动物。这些群体的作用鲜有研究，它们作为食鱼动物是否比鱼类更重要仍然未知。我们报告了对秘鲁马努国家公园洪泛区湖泊中鸟类、凯门鳄和巨型水獭种群的纵向（2001-2018）和横断面（2012）研究。在去除分类状态和体重的影响后，我们比较了三组，使用异速生长方程来估计每个湖中每组的野外代谢率 (FMR)。巨型水獭成为支持居民家庭的湖泊中的主要食鱼动物，能量需求是食鱼鸟类的两倍多，是凯门鳄的七倍多。然而，在被调查的 27 个湖泊中，只有 8 个栖息着巨型水獭。间接证据表明，这八个湖泊比没有被水獭占据的湖泊生产力更高。水獭占据的湖泊以浮游植物为主的事实表明，潜在的五层营养结构与食物网结构中交替水平的突出保持一致。