Data compilation
We used R2 values from linear fitting as indices of
species abundance estimation accuracy based on eDNA quantity because the
values were calculated in most studies collected in our meta-analysis.
If the manuscripts only reported Pearson’s correlation coefficients, we
squared the coefficients and substituted them for R2values. We then extracted the information on collection strategy
(filtration or centrifugation), quantification strategy
(species-specific or metabarcoding assay), target taxa, filter pore
sizes used for water filtration (μm), volume of water sample (mL), PCR
amplicon sizes (base pair; bp), study environments, and abundance
metrics (biomass or individuals) from the studies. As all the
metabarcoding studies in our meta-analysis collected aqueous eDNA by
filtration, collection and quantification strategy were combined as the
factor ‘assay strategy’, which was classified as
‘species-specific/filtration’, ‘species-specific/precipitation’, and
‘metabarcoding’. Taxa were classified as fish, herptiles (i.e., reptiles
and amphibians), crustaceans, mollusks, and coral and seastars. In
studies involving aqueous eDNA collection via centrifugation, the
filter pore size was regarded as 0 μm. Study environments were
classified as laboratory (i.e., tank, aquarium, or mesocosm
experiments), lentic freshwater, lotic freshwater, and marine
environments. Multiple R2 values based on different
experimental conditions within the same study (e.g., species, filter
type, and amplicon size) were treated individually. Moreover, we
calculated the sample size (the number of water samples or sampling
sites) required for calculating R2 values or
coefficients based on figures and/or text in the corresponding
literature.