Abstract

The sika deer (Cervus nippon), introduced or released for various purposes, has rapidly expanded its populations worldwide owing to its high environmental adaptability, and is now recognized as a major driver of ecological and economic damage in forests and farmlands. Island ecosystems are particularly vulnerable to invasive species because of their limited area, isolation, and high levels of native species; however, ecological research on the impacts of invasive sika deer remains scarce in Korea. Therefore, this study aimed to elucidate the feeding patterns of sika deer inhabiting three offshore islands of the Yellow Sea—Gureopdo, Nanjido, and Anmado—using fecal DNA metabarcoding. Between March and October 2024, a total of 45 fecal samples (15 per island) were collected, and dietary plant taxa were identified through DNA extraction and next-generation sequencing-based metabarcoding. The results revealed a strong dietary dependence on Carex in Gureopdo, a mixed feeding strategy involving both trees and herbs in Nanjido, and a wide range of resources including cultivated and ornamental plants in Anmado. These findings demonstrate that invasive sika deer adopt different feeding strategies depending on vegetation structure and environmental conditions, highlighting their potential impacts on island ecosystems. To our knowledge, this is the first study in Korea to clarify the feeding ecology of invasive sika deer using molecular techniques, providing baseline information for the development of integrated management strategies encompassing population control, habitat restoration, eDNA-based long-term monitoring, and community-based cooperation.