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, however, it is often unclear what metrics are used to support this claim. Over the past decade, there have been many direct comparative studies between eDNA and conventional methods. While several have found support for increased sensitivity and efficiency of eDNA methods, others have found the opposite, necessitating a review that synthesizes the outcomes of these comparisons. Here, we systematically review all comparative studies between eDNA and conventional survey methods published between 2008 and 2023. We review the various metrics used to evaluate the relative performance of eDNA methods, the relative performance of eDNA methods according to those metrics, and whether study characteristics influenced the outcome of the comparisons. Our review found that eDNA is more likely to provide increased estimates of sensitivity metrics, mainly species richness and detection probability. They also display lower estimates of efficiency metrics, including cost and sampling time/effort. However, despite repeated claims that eDNA allows for greater taxonomic resolution by distinguishing cryptic species, eDNA methods are more likely to yield lower estimates of taxonomic resolution. Trends in comparative outcomes were consistent across study environments, target taxa, sampled substrate, and levels of eDNA replication. However, we highlight multiple areas that have received little exploration into the relative performance of eDNA, including many environments of the global south and the ability of eDNA to monitor temporal changes in biodiversity. Our review provides a more comprehensive examination of eDNA comparative studies and delivers clarity to conservation professionals on where, when, and how eDNA methods are likely to carry substantial benefits in monitoring biodiversity.

This file contains the list of articles used for the systematic review, the information obtained from each article, and relevant metadata. All articles were obtained from Web of Science or were supplemented from the journals Environmental DNA, Metabarcoding, and Metagenomics. All articles were reviewed by the authors to verify that they met the definition of an Environmental DNA comparative study (see text). After initial review, articles were QC'd by another author to verify that the information was correct.