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Interspecific competition and predation: relative effects on foragers and their densities

机译：种间竞争和捕食：对觅食者及其密度的相对影响

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Predation and competition are both strong structuring forces in community dynamics, but their relative importance is disputed. In a laboratory experiment, we evaluated the relative importance of competition and predation from juvenile and adult brown trout, respectively, on foraging performance of groups of three stone loaches. We observed loach consumption rate, time spent inactive, and aggressive interactions between juvenile trout and loach in artificial stream sections. The controlled experiments were complemented by examining stone loach population densities in natural systems as functions of juvenile and adult trout. In the laboratory experiments, increasing numbers of competitors decreased prey availability, which ultimately led to lower consumption rates for loach. Loach responded to predation risk by increasing time being inactive, thereby decreasing consumption rates. However, there were no effects of juvenile trout competitors on loach consumption rates in treatments with adult trout presence, suggesting no additive effect of predation and competition on loach foraging success. Partial regressions of loach and trout densities in natural streams revealed a positive relationship between juvenile trout and loach, and a negative relationship between adult trout and loach. Our laboratory and field data thus suggest that predation is a limiting factor for loach success, and predator presence could mediate species coexistence at high interspecific densities.
机译：掠夺和竞争都是社区动态的强大结构力量，但它们的相对重要性却存在争议。在实验室实验中，我们评估了幼鱼和成年褐鳟的竞争和捕食对三个石lo群体觅食性能的相对重要性。我们观察了泥stream的消耗率，不活动的时间以及幼年鳟鱼和泥stream在人工溪流区域之间的侵略性相互作用。通过检查自然系统中幼年和成年鳟鱼的石stone种群密度来补充对照实验。在实验室实验中，竞争者数量的增加降低了猎物的可利用性，从而最终降低了泥consumption的食用率。泥ach通过增加不活动时间来应对捕食风险，从而降低了食用率。然而，在有成年鳟鱼存在的处理中，少年鳟鱼竞争者对泥consumption消耗率没有影响，表明捕食和竞争对泥ach觅食成功没有累加作用。天然溪流中泥ach和鳟鱼密度的部分回归显示，少年鳟鱼与泥ach之间呈正相关，而成年鳟鱼与泥lo之间呈负相关。因此，我们的实验室和现场数据表明，捕食是泥lo成功的限制因素，而捕食者的存在可以在高种间密度下介导物种共存。

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