Efficiency of eDNA and iDNA in assessing vertebrate diversity and its abundance

Environmental DNA (eDNA) and invertebrate-derived DNA (iDNA) have been increasingly recognized as a powerful tool for biodiversity assessment and conservation management. However, because of uncertainties on the efficiency of eDNA/iDNA approach in comparison to conventional methods, its use to assess the vertebrate diversity is still rare. Here we assessed the efficiency of eDNA/iDNA in comparison to conventional methods to survey vertebrate diversity across several type of samplers, vertebrate groups, and location (tropical vs temperate zones), as well as its efficiency to be used as a proxy for relative abundance or biomass across different molecular methods (qPCR and metabarcoding) and types of experiments (in the lab or in the field). The metanalysis showed that, in general, there is no difference in the number of species detected or number of sites that a target species was detected when using eDNA/iDNA or conventional methods, suggesting that eDNA/iDNA and conventional methods were equally efficient in characterizing the biodiversity. However, for water sampler and fish, separately, the risk of not finding a species was greater using conventional method than eDNA, suggesting that eDNA/iDNA was more efficient in finding the target species. Abundance and biomass showed similar correlation patterns, and there was a positive correlation between eDNA/iDNA and abundance/biomass data, suggesting that eDNA/iDNA can be used as a proxy for abundance and biomass. Therefore, eDNA/iDNA has proved to be an efficient tool to assess vertebrate diversity in terms of both diversity of species and abundance or biomass.