Huryn Alexander D
Department of Zoology, P.O. Box 56, University of Otago, Dunedin, New Zealand, , , , , , NZ.
Oecologia. 1998 Jun;115(1-2):173-183. doi: 10.1007/s004420050505.
Ecosystem-wide effects of introduced brown trout (Salmo trutta L.) and native river galaxias (Galaxiaseldoni McDowall) were studied by analysing ecosystem production budgets for two adjacent tributaries of a grassland stream-system in the South Island of New Zealand. One tributary was inhabited by brown trout, the other by river galaxias. No other fish species were present in either stream. The budget for the river galaxias stream indicated little top-down control of invertebrates by fish predation (river galaxias consumed ∼18% of available prey production). A large proportion of annual net primary production was required to support production by invertebrates (invertebrates consumed an average of ∼75% of available primary production), and mean surplus primary production (i.e. not consumed) was not significantly different from zero. Primary and secondary production were presumably mutually limiting in this system (i.e. controlled by simultaneous top-down and bottom-up mechanisms). In contrast, the budget for the brown trout stream indicated extreme top-down control of invertebrate populations by fish predation; essentially all invertebrate production (∼100%) was required to support trout production. Invertebrate production required only a minor portion of annual net primary production (∼21%) and primary production was presumably controlled by mechanisms other than grazing (e.g. sloughing, nutrient limitation). Predatory invertebrates had little quantitative effect on prey populations in either stream. Recent experimental studies of invertebrate behaviour, fish behaviour, and food-web structure in New Zealand streams with physically stable channels indicate that a trophic cascade should be observed in streams inhabited by brown trout, in contrast to those inhabited by native fish. The results reported here provide ecosystem-level evidence supporting this prediction.
通过分析新西兰南岛一个草原溪流系统中两条相邻支流的生态系统生产预算，研究了引入的褐鳟（Salmo trutta L.）和本地河鲈（Galaxiaseldoni McDowall）对整个生态系统的影响。一条支流中有褐鳟栖息，另一条中有河鲈栖息。两条溪流中均未出现其他鱼类物种。河鲈溪流的预算表明，鱼类捕食对无脊椎动物的自上而下控制作用较小（河鲈消耗了约18%的可利用猎物产量）。需要很大一部分年净初级生产量来支持无脊椎动物的生产（无脊椎动物平均消耗了约75%的可利用初级生产量），并且平均剩余初级生产量（即未被消耗的量）与零没有显著差异。在这个系统中，初级生产和次级生产可能相互限制（即由同时存在的自上而下和自下而上机制控制）。相比之下，褐鳟溪流的预算表明，鱼类捕食对无脊椎动物种群有极强的自上而下控制作用；基本上所有无脊椎动物的产量（约100%）都被用于支持褐鳟的生产。无脊椎动物的生产仅需要年净初级生产量的一小部分（约21%），并且初级生产可能受除放牧之外的其他机制控制（例如脱落、养分限制）。捕食性无脊椎动物对两条溪流中的猎物种群数量影响都很小。最近在新西兰具有物理稳定河道的溪流中对无脊椎动物行为、鱼类行为和食物网结构进行的实验研究表明，与本地鱼类栖息的溪流相比，在褐鳟栖息的溪流中应该会观察到营养级联现象。此处报告的结果提供了支持这一预测的生态系统层面的证据。
