Population structure impacts the relationship between the amount of environmental DNA particles and organism abundance

1. To achieve the precise estimation of organism abundance using environmental DNA (eDNA) analysis, factors affecting the relationship between the amount of eDNA particles and organism abundance should be understood. Wild populations often exhibit a broad range of individual density and body size structure, which can affect the population-level eDNA production. However, it remains unknown how the eDNA-abundance relationship is linked to such population characteristics.2. This study conducted a numerical simulation to assess the effects of population size and structure on the relationship between the amount of eDNA particles and population abundance. The simulation results were further compared between different abundance metrics (biomass or allometric scaled mass [ASM]) and eDNA production scenarios (linear or allometric relationship with body mass).3. The strength of the eDNA-abundance relationship (<i>R</i>^<em>2</em> value in linear regression) was positively associated with the factors determining the number of individuals, mean body mass, and mass variation in each site. The <i>R</i>^<em>2</em> values were generally higher by using ASM than biomass when eDNA production was scaled allometrically with body mass, but rather lower when eDNA production was scaled linearly with body mass.4. These factors also formed complex interactions on the eDNA-abundance relationship. The mean body mass and mass variation interactively increased the <i>R</i>^<em>2</em> value. On the other hand, under the allometric eDNA production, the <i>R</i>^<em>2</em> values decreased for the populations with broader population size range and broader/heterogeneous mass distribution by using biomass, which was not statistically significant by using ASM.5. <i>Synthesis and applications</i>: The present simulation demonstrated that the strength of the eDNA-abundance relationship complicatedly relied on the population size and structure. This study gives insights into explaining the uncertainties inherent in the eDNA-abundance relationship in the field, and underpins the importance of integrating allometric scaling into population-level eDNA production to improve the eDNA-based abundance estimation. To make the findings more valid and robust, further empirical studies are encouraged to examine how eDNA production is linked to organism’s physiology and ecology and whether eDNA production is scaled allometrically with body mass.

1. 若要通过环境DNA（environmental DNA, eDNA）分析实现生物丰度的精准估算，需明确影响eDNA颗粒数量与生物丰度之间关联的各类因素。野生种群通常具有宽泛的个体密度与体型结构范围，这会对种群水平的eDNA产生量造成影响，但目前仍不清楚eDNA-丰度关联与这类种群特征之间的具体联系。
2. 本研究通过数值模拟评估了种群规模与结构对eDNA颗粒数量与种群丰度之间关联的影响，并针对不同丰度指标（生物量或异速标度质量（allometric scaled mass, ASM)）以及eDNA产生情景（与体重呈线性或异速相关关系）下的模拟结果展开了对比分析。
3. eDNA-丰度关联的强度（即线性回归中的决定系数R²）与每个样地的个体数量、平均体重及体重变异等因素呈正相关。当eDNA产生量按体重进行异速标度时，采用ASM计算得到的R²值通常高于生物量；而当eDNA产生量与体重呈线性标度关系时，采用ASM得到的R²值则相对更低。
4. 上述因素还会对eDNA-丰度关联产生复杂的交互影响。平均体重与体重变异可通过交互作用提升R²值。而在eDNA产生呈异速标度的情况下，当种群规模范围更广、体重分布更宽泛/异质性更强时，采用生物量计算得到的R²值会出现下降，但采用ASM时该变化未达到统计学显著性水平。
5. 综合与应用：本模拟研究表明，eDNA-丰度关联的强度复杂地依赖于种群规模与结构。本研究为解释野外环境中eDNA-丰度关联固有的不确定性提供了思路，并凸显了将异速标度整合至种群水平eDNA产生过程的重要性，以优化基于eDNA的生物丰度估算方法。为使研究结论更具有效性与稳健性，未来亟需开展更多实证研究，以明确eDNA产生与生物生理及生态特征之间的关联，同时验证eDNA产生量是否可按体重进行异速标度。