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 (R² 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 R² 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 R² value. On the other hand, under the allometric eDNA production, the R² 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. Synthesis and applications: 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.