Invasive rats and threatened lizards on islands: a DNA metabarcoding approach to assess dietary spectra and trophic interactions on the Aeolian archipelago

Abstract

Island ecosystems often host endemics that are highly vulnerable to invasive species. In the Mediterranean biodiversity hotspot, the Endangered Aeolian wall lizard Podarcis raffonei is undergoing severe population decline. Its largest remaining population, on Vulcano Island, dropped by c. 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 of faecal samples, we investigated potential trophic interactions between rats and lizards on Vulcano and provided a detailed characterization of the lizard’s 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; they showed a limited dietary overlap with lizards for animal resources but a high dietary overlap for plant resources. 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.