Preservative Ethanol From Stomach Contents Is a Reliable Proxy for Diet DNA Metabarcoding

ABSTRACT Reliable dietary data are essential for understanding trophic interactions and the impacts of invasive predators. Stomach contents from hunted animals can provide direct evidence of diet while avoiding dedicated culling, but transporting them from remote areas is logistically challenging. We tested whether DNA metabarcoding of preservative ethanol from stomach contents could substitute for bulk stomach content, using mona monkeys introduced to the island nation of São Tomé and Príncipe as a case study. Two DNA extraction methods were applied to reconstruct diets from preservative ethanol (Precipitation and Drying). Stomachs were obtained from local bushmeat hunters, who retained them at our request as by‐products of routine hunting. Diet profiles were generated using animal COI and plant ITS2 markers. Ethanol‐derived profiles retrieved slightly higher sample richness, but the population‐level diet closely matched that obtained from bulk stomach content. Read counts per OTU were similar across matrices, and discrepancies were largely confined to low‐read detections. Comparisons between two DNA extraction methods revealed no major differences in per‐sample richness or composition. Precipitation reduced detections of incidental prey, notably Diptera, without altering the core diet composition, whereas drying recovered more OTUs by increasing taxa with low‐read counts. The reconstructed diet was highly generalist, dominated by fruiting plants and arthropods, many of which likely reflected secondary ingestion. Vertebrates occurred in 9% of samples and included endemic birds and lizards. Together, these results validate preservative ethanol as a practical proxy for bulk stomach contents when reconstructing the main components of omnivore diets in remote island contexts. We recommend precipitation for conservative reconstructions of primary diets and drying when maximizing detections of rare taxa. This approach reduces storage and transport constraints, enabling scalable and comparable dietary monitoring to inform assessments of invasive primate impacts on native faunas.