Dahl Jonas
Department of Ecology, Limnology, Ecology Building, S-223 62 Lund, Sweden e-mail:
Oecologia. 1998 Sep;116(3):426-432. doi: 10.1007/s004420050606.
I assessed the impact of both drift-feeding (Salmo trutta, brown trout) and benthic-feeding (Cottus gobio, bullhead) fish on a benthic assemblage during a 1-month-long field experiment. I used enclosures containing cobble/gravel substrata with 6-mm mesh net that allowed invertebrates to drift freely in and out of enclosures. Four treatments, arranged in a factorial design, were tested: a predator-free control, bullheads only (2.67 bullheads/m, two per enclosure), brown trout only (2.67 brown trout/m, two per enclosure), and bullheads and brown trout together (2.67 fish/m, one of each). Bullheads reduced the densities of seven invertebrate taxa (Gammarus pulex amphipods, Baetis rhodani mayfly nymphs, Leuctra spp. stonefly nymphs, Polycentropus spp. caddis larvae, Pacifastacus leniusculus signal crayfishes, Simuliidae, blackfly larvae, and Limnephilidae, caddis larvae) whereas brown trout only affected one taxon (B. rhodani). The weaker effect of brown trout on benthic prey was probably related to its heavy reliance on terrestrial prey. Dietary analyses showed that more than 80% of prey consumed by brown trout were terrestrial animals, whereas bullhead only consumed benthic prey. Neither bullhead nor brown trout affected the absolute number of immigrating or emigrating invertebrates in enclosures, but bullhead affected the per capita emigration rates of G. pulex. Direct predation by bullhead was more important than avoidance behaviour (drift) in determining densities of six of the seven taxa; only G. pulex densities were equally affected by avoidance behaviour and direct predation. Direct predation by brown trout was also more important in determining densities of B. rhodani. The presence of bullhead raised periphyton biomass, presumably mediated via their consumption of grazers. Brown trout had no effect on periphyton biomass and these results indicate that the presence of alternative prey, in this case terrestrial animals, may have repercussions for fish-benthic macroinvertebrate-periphyton interactions and may potentially explain some of the variable impacts of fish on benthic macroinvertebrates that have been reported in the literature.
在一项为期1个月的野外实验中，我评估了漂流取食鱼类（褐鳟）和底栖取食鱼类（欧洲牛尾鱼）对底栖生物群落的影响。我使用了装有卵石/砾石基质的围隔，围隔带有6毫米网眼的网，允许无脊椎动物自由进出围隔。实验采用析因设计，测试了四种处理方式：无捕食者对照、仅放入欧洲牛尾鱼（2.67条/米，每个围隔两条）、仅放入褐鳟（2.67条/米，每个围隔两条）以及同时放入欧洲牛尾鱼和褐鳟（2.67条/米，每种各一条）。欧洲牛尾鱼降低了7个无脊椎动物类群的密度（蚤状钩虾、红纹蜉蝣若虫、小石蝇若虫、多距石蛾幼虫、信号螯虾、蚋科幼虫和沼石蛾幼虫），而褐鳟仅影响了一个类群（红纹蜉蝣）。褐鳟对底栖猎物的影响较弱可能与其对陆生猎物的严重依赖有关。饮食分析表明，褐鳟所消耗猎物中超过80%是陆生动物，而欧洲牛尾鱼只捕食底栖猎物。欧洲牛尾鱼和褐鳟都没有影响围隔中迁入或迁出的无脊椎动物的绝对数量，但欧洲牛尾鱼影响了蚤状钩虾的人均迁出率。在决定7个类群中6个类群的密度时，欧洲牛尾鱼的直接捕食比回避行为（漂流）更重要；只有蚤状钩虾的密度受回避行为和直接捕食的影响程度相同。褐鳟的直接捕食在决定红纹蜉蝣的密度时也更重要。欧洲牛尾鱼的存在增加了周丛生物量，推测是通过它们对食草动物的捕食介导的。褐鳟对周丛生物量没有影响，这些结果表明，替代猎物（在这种情况下是陆生动物）的存在可能会对鱼类 - 底栖大型无脊椎动物 - 周丛生物的相互作用产生影响，并可能潜在地解释了文献中报道的鱼类对底栖大型无脊椎动物的一些可变影响。
