Developing fast, cost-effective assessments of wild animal abundance is an important goal for many researchers, and environmental DNA (eDNA) holds much promise for this purpose. However, the quantitative relationship between species abundance and the amount of DNA present in the environment is likely to vary substantially among taxa and with ecological context. Here, we report a strong quantitative relationship between eDNA concentration and the abundance of spawning sockeye salmon in a small stream in Alaska, USA, where we took temporally- and spatially-replicated samples during the spawning period. This high-resolution dataset suggests that (1) eDNA concentrations vary significantly day-to-day, and likely within hours, in the context of the dynamic biological event of a salmon spawning season; (2) eDNA, as detected by species-specific quantitative PCR probes, seems to be conserved over short distances (tens of meters) in running water, but degrade quickly over larger scales (ca. 1.5 km); and (3) factors other than the mere presence of live, individual fish — such as location within the stream, live/dead ratio, and water temperature — can affect the eDNA-biomass correlation in space or time. A multivariate model incorporating both biotic and abiotic variables accounted for over 75% of the eDNA variance observed, suggesting that where a system is well-characterized, it may be possible to predict species' abundance from eDNA surveys, although we underscore that species- and system-specific variables are likely to limit the generality of any given quantitative model. Nevertheless, these findings provide an important step toward quantitative applications of eDNA in conservation and management.

中文翻译：

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环境 DNA (eDNA) 的浓度反映了精细空间和时间尺度上产卵鲑鱼的丰度

对野生动物丰度进行快速、经济高效的评估是许多研究人员的一个重要目标，而环境 DNA (eDNA) 对此有很大希望。然而，物种丰度与环境中存在的 DNA 量之间的定量关系可能因类群和生态背景而有很大差异。在这里，我们报告了美国阿拉斯加一条小溪中的 eDNA 浓度与产卵红鲑鱼的丰度之间存在很强的定量关系，我们在产卵期间采集了时间和空间复制的样本。该高分辨率数据集表明：(1) 在鲑鱼产卵季节的动态生物事件背景下，eDNA 浓度每天都有显着变化，而且很可能在数小时内变化； (2) 通过物种特异性定量 PCR 探针检测到的 eDNA 似乎在流水中短距离（数十米）内保存，但在较大尺度（约 1.5 公里）内快速降解； (3) 除了活体个体鱼的存在之外，其他因素（例如溪流中的位置、活/死比和水温）也可能影响 eDNA-生物量在空间或时间上的相关性。包含生物和非生物变量的多变量模型占观察到的 eDNA 方差的 75% 以上，这表明在系统特征良好的情况下，可以通过 eDNA 调查来预测物种的丰度，尽管我们强调物种和系统特定的变量可能会限制任何给定定量模型的通用性。尽管如此，这些发现为 eDNA 在保护和管理中的定量应用迈出了重要一步。