Preface: Advances in Research on the Evolution, Ecology, and Conservation of Ryukyu Endemic Mammals

Shun Kobayashi, Mugino O. Kubo, Shoji Hayashi

The Ryukyu Archipelago stretches approximately 1500 km from north to south and consists of islands of various sizes. The region has a complex geological history, characterized by periods of isolation and reconnection with the mainland. Despite being situated in the predominantly arid subtropical zone, the archipelago features a humid climate and experiences periodic typhoons that cause medium-scale disturbances (Government of Japan 2019). These unique geological and environmental factors have resulted in a high degree of biodiversity, with many endemic species and subspecies inhabiting the region. Research on the biota of the Ryukyus has primarily focused on elucidating the archipelago's uniqueness and the factors contributing to its exceptional biodiversity. Furthermore, the region offers an invaluable opportunity for insular biology studies by enabling comparisons of islands with different isolation timelines, as well as comparisons between island and mainland species.
Recent conservation efforts, such as forest restoration and invasive species management, have facilitated the recovery of populations of species that were once difficult to study (e.g., Izawa and Yamada 2023). This has opened new avenues for comparative studies in ecology, morphology, and evolution. Long-term research and the adoption of advanced technologies are also expanding our understanding of these ecosystems. In 1993, “Yakushima” in the North Ryukyus was registered as a UNESCO World Heritage Site, followed in 2021 by “Amami-Oshima Island, Tokunoshima Island, Northern Part of Okinawa Island, and Iriomote Island” in the Central and South Ryukyus. Seventeen native mammal species are distributed on the former designated site (Ministry of the Environment et al. 2024) and 22 native mammal species on the latter site (Government of Japan 2019), and several introduced mammals have been established (Fig. 1). While the World Heritage designation underscores the unique biodiversity of these regions, it also highlights their vulnerability, necessitating robust conservation strategies. Conservation efforts should not, however, be limited to the designated areas, as many other islands also represent the biodiversity of the Ryukyus. Given the high number of inhabited and tourist-centric islands in the region, sustainable management strategies must address habitat conservation, ecology of native species, and problems on invasive species. The Ryukyus have recently emerged as a global model for invasive species management research (Ministry of the Environment 2024). Despite these advances, research focused on the conservation biology of native mammals remains limited. Understanding the specific traits of individual species is critical for guiding conservation efforts.
Amid these developments, the 100th-anniversary annual meeting of the Mammal Society of Japan was held in Okinawa in 2023. During the meeting, a workshop titled “Unveiling the Ecology of Endemic Mammals in the Ryukyu Islands” was organized by the contributors to this special issue. The content presented at the workshop has been further developed and compiled into this volume, which provides a comprehensive overview of mammalian research in the Ryukyu Archipelago, with a particular focus on the Central Ryukyus, whose World Heritage designation has heightened their global significance. Contributions from experienced researchers and graduate students are included, showcasing diverse perspectives on the natural history of mammals through eight papers.
The opening article, published as a part of Series of Reviews for Mammal Ecology in Japan celebrating the 50th volume of Mammal Study, offers a comprehensive review of the history and trends in mammalian research within the Ryukyus. It focuses on the Central and South Ryukyus, which were inscribed as World Heritage Sites in 2021 (Yamada and Izawa 2025, pp. 109–141). This review serves as a critical for understanding the region's research history and current challenges. Publishing this localized research history in English makes it accessible to international audiences, further enhancing its significance.

Three studies focus on life history traits. Hayashi and Kubo (2025, pp. 159–170) investigate the life history characteristics of Cervus nippon populations in the Ryukyus through bone histology, uncovering a shift toward slow life history traits in both native and introduced populations. Hayashi et al. (2025, pp. 171–184) analyze skeletal specimens of the Amami rabbit to provide insights into its unique life history traits and functional adaptations. Nakanishi et al. (2025, pp. 211–218) propose a method for estimating age stages in the Ryukyu long-furred rat based on tooth wear and skull size, offering a valuable foundation for future life history studies.
Two papers examine dietary ecology. Kobayashi et al. (2025, pp. 185–198) use the DNA metabarcoding to analyze the stomach contents of the Ryukyu long-furred rat, revealing a broader dietary range than previously reported. Kubo et al. (2025, pp. 199–210) use dental microwear analysis to assess seasonal dietary variation in the Amami rabbit and the Ryukyu long-furred rat. Both studies demonstrate the effectiveness of integrating multiple methodologies to better understand dietary variation and the ecological niche of these species.
The issue emphasizes the value of museum specimens in ecological and conservation research, while also underscoring the irreplaceable insights gained from field observations. For instance, Higashi and Kobayashi (2025, pp. 219–226) record predation by the habu snake (Protobothrops flavoviridis) on the Ryukyu long-furred rat through nest box monitoring. Such observations provide critical ecological information that cannot be inferred solely from specimen-based studies.
Each paper in this special issue contributes to understanding the unique characteristics of mammals in the Ryukyus and broader trends in island mammalian evolution. These findings are expected to form the basis for further research in insular biology, conservation, and sustainable management in the Ryukyu Archipelago. Although this special issue does not include studies on bats, which also exhibit high levels of diversity and endemism in the Ryukyus, researches of them are progressing and will be reported in the future.
Recent large-scale studies have demonstrated that species with higher degrees of insular adaptation face greater extinction risks due to human activities (Rozzi et al. 2023). By providing critical insights into the basic ecology and conservation needs of mammals in the Ryukyus, this special issue aims to guide future research and conservation efforts, offering valuable information to researchers worldwide.

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