A systematic review evaluating the performance of eDNA methods relative to conventional methods for biodiversity monitoring

Abstract

The rapid adoption of environmental DNA (eDNA) methods has drastically changed biodiversity monitoring efforts. It is often claimed that eDNA methods are more sensitive and efficient than conventional biodiversity monitoring methods, but it is often unclear what metrics support this claim. There have been many direct comparative studies between eDNA and conventional methods; several supporting the increased sensitivity and efficiency of eDNA methods, others finding the opposite.Here, we systematically review all comparative studies between eDNA and conventional methods published between 2008 and 2023. We review various metrics used to evaluate the relative performance of eDNA methods and whether study characteristics influenced comparative outcomes. We found that eDNA is more likely to provide increased estimates of sensitivity metrics (i.e. species richness and detection probability) and lower estimates of efficiency metrics (i.e. cost and sampling time/effort). However, eDNA methods displayed their own biases, often recovering communities distinct from those revealed via conventional methods. While eDNA methods were capable of describing abundance and improving taxonomic resolution, we observed substantial variation. Trends in comparative outcomes were consistent across study characteristics, but we highlight areas that have received little exploration into the relative performance of eDNA, including across much of the Global South and the ability of eDNA to monitor temporal changes in biodiversity. Our review provides a comprehensive examination of eDNA comparative studies and delivers clarity to conservation professionals on where, when, and how eDNA methods are likely to add value to biodiversity monitoring initiatives.