DNA metabarcoding dietary spectra of Aeolian Archipelago

Island ecosystems often host endemic diversity that is highly vulnerable to invasive species. In the Mediterranean biodiversity hotspot, the Critically Endangered Aeolian wall lizard (Podarcis raffonei) is undergoing severe population decline. Its largest remaining population on Vulcano Island has dropped by roughly 60% from 2017 to 2022. A newly identified threat is the invasive black rat (Rattus rattus), recently recorded at high densities in the area. Using DNA metabarcoding on faecal samples, we investigated potential trophic interactions between rats and lizards on Vulcano and provided a detailed characterization of lizard diet across three populations. Podarcis raffonei primarily consumed arthropods (65.7%), particularly Hymenoptera, Hemiptera, and Lepidoptera, but also a significant proportion of plant matter (34.3%) including Asterales, Fabales, and Poales. Rats exhibited a similarly broad diet and showed limited dietary overlap with lizards for animal resources (Pianka index = 0.50, P = 0.239) but high dietary overlap for plant resources (Pianka index = 0.815, P = 0.006), though no lizard DNA was found in rat faeces. These findings suggest that trophic competition, rather than direct predation, may be a key driver of the lizard's decline. This study highlights the power of DNA metabarcoding to reveal cryptic ecological interactions and provides crucial insights for urgent conservation measures, including rat control and habitat management under the LIFE EOLIZARD project (101114121 LIFE22-NAT-IT-LIFE EOLIZARD).