Estimation accuracy and environments
Higher R2 values were reported for laboratory
conditions than natural environments, which is consistent with previous
findings (Yates et al., 2019) and supports the methodological validity
of our statistical analyses. As discussed in Yates et al. (2019), myriad
and complex dynamics of eDNA could hamper the prediction of species
abundance based on eDNA concentration in natural relative to controlled
environments. However, we observed little difference in estimation
accuracy among natural environments. Relative to lentic freshwater
environments, such as ponds and lakes, eDNA diffusion and degradation
would be substantial in riverine, coastal, and marine environments due
to flow and tidal effects. Such factors can transport eDNA very long
distances (Deiner & Altermatt, 2014; Andruszkiewicz et al., 2019) while
also resulting in rapid dilution (Baker et al., 2018). In contrast,
although eDNA may diffuse less in lentic environments (Fremier et al.,
2019; Curtis et al., 2020), residual eDNA may cause false-positive
inferences of species presence and inaccurate estimation of species
abundance. It is noted that our results must be cautiously interpreted
given the bias in the number of studies among natural environment types,
but eDNA-based abundance estimation accuracy might not necessarily be
worsened for lotic freshwater and marine environments relative to lentic
environments.