Properties and limitations of eDNA substrates for terrestrial animal monitoring

Environmental DNA (eDNA) has emerged as a crucial tool for monitoring terrestrial animals, yet numerous variables can influence species detection. Among these, the choice of sampling substrate and method is paramount and should align with the specific research objectives. This review provides a thorough overview of eDNA sampling methods and substrates, focusing on their effectiveness in detecting species across various spatiotemporal scales. We categorize substrates into three groups: abiotic substrates (soil, water, air, sediment), biotic substrates (invertebrate, scat, spiderweb, plant tissue, plant swab), and direct-trace substrates (artificial setups, feeding trace, animal track, tree hollow, bird nest, saltlick). Additionally, we address key processes leading to false-negatives and false-positives due to spatial and temporal deviations between the eDNA source and the sampling. Practical considerations for designing sampling plans are also discussed, including strategies to enhance detection accuracy and considerations tailored to specific taxa and habitats.