Diet of invasive cats, rats and tegu lizards reveals impact over threatened species in a tropical island

• Published in: Perspectives in Ecology and Conservation
• Main Authors: Juliana Vallim Gaiotto, Carlos Roberto Abrahão, Ricardo Augusto Dias, Leandro Bugoni
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2020
• Subjects: Management; Seabirds; Skink; Stable isotopes; Trophic ecology; Ecology; QH540-549.5; General. Including nature conservation; geographical distribution; QH1-199.5; Rattus rattus
• Online Access: https://doi.org/10.1016/j.pecon.2020.09.005; https://doaj.org/article/a7ff084a457c49d3a5a8869cdab31b52

Vertebrates introduced in non-native habitats have contributed to several extinctions in the modern era, with direct effects mainly over birds, mammals and reptiles on islands. Fernando de Noronha Archipelago, in tropical Atlantic Ocean, is a World Heritage natural site, holding the most diverse breeding seabird community off Brazil, in addition to endemic landbirds and reptiles. It also holds invasive black rats (Rattus rattus), tegu lizards (Salvator merianae) and feral cats (Felis catus), among the 26 exotic species reported in the archipelago, all of which are species with potentially high impact upon native fauna. Aiming to assess the role of exotic vertebrates on the fauna, we investigated their diets through stomach content and scat analysis, and stable isotope analysis (SIA) followed by isotopic mixing models. The main food items for tegu lizards were fruits, with relative importance (Prey-specific Index of Relative Importance – %PSIRI) of 41.3%, and the endemic Noronha skink (Trachylepis atlantica; 19.6%) and for black rats was Noronha skink (30.3%). The diet of feral cats was composed by rodents (31.6%), birds (28.6%) and Noronha skink (18.8%). SIA and Bayesian mixing models provided evidences that invasive species use marine matter to synthesize tissues, probably derived directly or indirectly from seabird colonies. This study demonstrated that exotic species feed on other exotic, as well as endemic species. The most heavily impacted species was the endemic Noronha skink. We demonstrated the predation pressure of exotic fauna upon endemic vertebrates, and strongly recommend the implementation of an invasive species control and eradication plan.