ABSTRACT: Variation in the energy content of prey can drive the diet choice, growth and ultimate survival of consumers. In Pacific salmon species, obtaining sufficient energy for rapid growth during early marine residence is hypothesized to reduce the risk of size-selective mortality. In order to determine the energetic benefit of feeding choices for individuals, accurate estimates of energy density (ED) across prey groups are required. Frequently, a single species is assumed to be representative of a larger taxonomic group or related species. Further, single-point estimates are often assumed to be representative of a group across seasons, despite temporal variability. To test the validity of these practices, we sampled zooplankton prey of juvenile Chinook salmon to investigate fine-scale taxonomic and temporal differences in ED. Using a recently developed model to estimate the ED of organisms using percent ash-free dry weight, we compared energy content of several groups that are typically grouped together in growth studies. Decapod megalopae were more energy rich than zoeae and showed family-level variability in ED. Amphipods showed significant species-level variability in ED. Temporal differences were observed, but patterns were not consistent among groups. Bioenergetic model simulations showed that growth rate of juvenile Chinook salmon was almost identical when prey ED values were calculated on a fine scale or on a taxon-averaged coarse scale. However, single-species representative calculations of prey ED yielded highly variable output in growth depending on the representative species used. These results suggest that the latter approach may yield significantly biased results.

中文翻译：

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奇努克鲑鱼Oncorhynchus tshawytscha的无脊椎动物猎物能量密度的精细分类和时间变化

摘要：猎物能量含量的变化可以驱动饮食的选择，增长和最终消费者的生存。在太平洋鲑鱼物种中，假设能够获得足够的能量以在早期海洋居住期间快速生长，以降低按大小选择死亡的风险。为了确定个体喂养选择的能量效益，需要准确估计整个猎物群的能量密度（ED）。通常，单个物种被认为是更大的分类组或相关物种的代表。此外，尽管时间上存在可变性，但通常假设单点估计值代表整个季节中的一组。为了验证这些做法的有效性，我们对幼稚的奇努克鲑鱼进行了浮游动物捕捞，以调查ED中的细微分类和时间差异。我们使用最近开发的模型使用无灰干重百分比估算生物体的ED，我们比较了在生长研究中通常分组在一起的几组能量含量。十足足动物比动物更富有能量，并且在ED中表现出家庭水平的变异性。两栖动物在ED中显示出明显的物种水平变异性。观察到时间差异，但各组之间的模式不一致。生物能模型模拟表明，当以细规模或分类单元平均粗规模计算猎物ED值时，奇努克鲑幼鱼的生长速率几乎相同。但是，根据所使用的代表性物种，对捕食者ED进行单物种代表性计算得出的生长产量变化很大。