1. A positive relationship between body size and trophic position is often assumed in ecology, but efforts to confirm the generality of this relationship for freshwater vertebrates have produced mixed results. Some authors have tested for among‐species relationships, using species‐level estimates of average size and trophic position. Others have used individual‐level body size and trophic position data to test for within‐species relationships. However, no study has yet estimated prevalence, defined here as the fraction of total standing stock biomass within a given ecosystem that consists of taxa exhibiting positive size versus trophic position relationships.
2. Individual‐level estimates of body size and relative trophic position (inferred from bulk‐tissue nitrogen stable isotopes) were collected for vertebrates in six temperate streams. In each stream, all locally occurring vertebrate taxa were collected and closed population depletion samples were used to obtain standing stock biomass estimates.
3. Ordinary least squares regression was used with the individual‐level data to test for positive relationships between body size and relative trophic position (r‐STPRs). A separate r‐STPR model was tested for each vertebrate species collected at the six study sites. Linear mixed‐effects modelling was then used to test for differing r‐STPRs among species.
4. Prevalence of the r‐STPR was calculated for each site by summing the standing stock biomass of all taxa that exhibited a statistically significant, positive STPR at a given site, then dividing this number by the total standing stock biomass of vertebrates at the site.
5. Significant, positive r‐STPRs were detected in 15 of 22 species × site regression models. Prevalence of species with positive r‐STPRs ranged from 91 to 100% of the total vertebrate biomass in western streams and from 45 to 66% in eastern streams.
6. Results confirm that positive r‐STPRs are characteristic of many of the vertebrate taxa considered in this study. Furthermore, species that exhibit positive r‐STPRs comprise a clear majority of the standing stock biomass in five of six study streams. By using individual‐level data to account for prevalence, a more complete understanding of size‐dependent trophic dynamics should be possible in freshwater ecosystems.

中文翻译：

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个体水平的数据显示，温带河流中脊椎动物的正向大小营养位置关系普遍存在

1. 在生态学中，通常认为体型与营养位置之间存在正相关关系，但为确认淡水脊椎动物的这种关系的普遍性而做出的努力却产生了不同的结果。一些作者使用物种水平的平均大小和营养位置估计对物种间的关系进行了测试。其他人则使用个体水平的体重和营养位置数据来测试种内关系。然而，尚无研究估计流行率，在此将流行率定义为给定生态系统中总站立生物量的比例，该生态系统由显示正大小与营养位置关系的类群组成。
2. 从六个温带流域中的脊椎动物中收集了个体水平的个体大小和相对营养位置的估计值（从大块组织中的氮稳定同位素推断）。在每个流中，收集了所有本地出现的脊椎动物类群，并使用了封闭的种群耗竭样本来获得常规种群生物量的估计值。
3. 将普通最小二乘回归与个人水平数据一起使用，以检验体重与相对营养位置（r- STPR）之间的正相关关系。对在六个研究地点收集的每种脊椎动物进行了单独的r- STPR模型测试。然后，使用线性混合效应模型来测试物种之间不同的r- STPR。
4. 通过将在给定位置显示出统计学上显着的正STPR的所有分类单元的立足生物量相加，然后除以该站点脊椎动物的立足生物量总量，可以计算出每个站点的r- STPR患病率。
5. 在22种×位点回归模型中的15种中检测到了显着的正r- STPRs。r- STPRs阳性的物种在西部流域的脊椎动物生物量的比例为91％至100％，在东部流域的比例为45％至66％。
6. 结果证实，本研究中考虑的许多脊椎动物类群均具有阳性的r- STPRs。此外，在六个研究流中的五个中，表现出正r- STPR的物种构成了常规生物量的绝大部分。通过使用个体水平的数据来解释流行程度，在淡水生态系统中应该有可能对大小相关的营养动力学有更完整的了解。