Iijima Daichi, Ando Haruko, Inoue Tohki, Murakami Masashi, Ito Shun, Fukuda Shinpei, Sato Nozomu J
Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, Hachioji, Japan.
Izu Islands Ornithological Research Group, Yokohama, Japan.
J Anim Ecol. 2025 Jun 25. doi: 10.1111/1365-2656.70070.
Oceanic island ecosystems are highly vulnerable to human activities. Oceanic islands near the mainland offer insights into natural processes, including overseas dispersal from the mainland. However, most studies examining community changes on oceanic islands focus on human activities, while natural colonisation from the mainland has received limited attention. To clarify the mechanisms of insular community changes due to human activities and natural colonisation, we investigated bird assemblages on 10 islands during 2016 and 2021 and compared them to the assemblages during 1970 and 1973 on the Izu Islands, Japan. We explored how the species traits and mainland distribution changes of species are associated with distribution changes of each species on the 10 islands using phylogenetic generalised least squares (PGLS). Furthermore, bird community structures on each island were examined based on species richness and functional and phylogenetic structures. A null modelling approach was used to examine functional and phylogenetic cluster/overdispersion structures; clustering and overdispersion imply environmental filtering and limiting similarity, respectively. We analysed the effects of geographical and topographical characteristics of the islands, introduced predators and human-induced landscape transformations on changes in community structures using linear models (LMs). Species that expanded their mainland distribution and with large clutches colonised many islands. Raptors disappeared from many islands. Species richness decreased, and functional and phylogenetic structures became clustered on almost all islands, which were only statistically associated with geographical and topographical characteristics. The distribution changes in species on islands were associated with their mainland distribution changes, which indicates that mainland community dynamics influence insular communities via overseas colonisation. Despite the colonisations, the net loss of species richness, clustered phylogenetic and functional structures, and disappearance of top predators on many islands suggest that bird communities across the archipelago degraded. Previous studies have demonstrated that introduced weasels negatively affect birds through competition for food resources and direct predation on the introduced islands. These degraded bird communities due to introduced weasels would have transboundary biodiversity effects on communities across the archipelago via inter-island movements of birds, which suggests the need for comprehensive conservation strategies across the archipelago to effectively conserve insular biodiversity.
大洋岛屿生态系统极易受到人类活动的影响。靠近大陆的大洋岛屿为自然过程提供了见解，包括从大陆的海外扩散。然而，大多数研究大洋岛屿群落变化的研究都集中在人类活动上，而来自大陆的自然定殖受到的关注有限。为了阐明人类活动和自然定殖导致岛屿群落变化的机制，我们在2016年至2021年期间调查了10个岛屿上的鸟类群落，并将它们与1970年至1973年日本伊豆群岛上的鸟类群落进行了比较。我们使用系统发育广义最小二乘法（PGLS）探索了物种的性状和大陆分布变化如何与这10个岛屿上每个物种的分布变化相关联。此外，基于物种丰富度以及功能和系统发育结构，对每个岛屿上的鸟类群落结构进行了研究。采用零模型方法来研究功能和系统发育聚类/过分散结构；聚类和过分散分别意味着环境过滤和限制相似性。我们使用线性模型（LMs）分析了岛屿的地理和地形特征、引入的捕食者以及人类引起的景观变化对群落结构变化的影响。在大陆分布范围扩大且窝卵数多的物种在许多岛屿上定殖。猛禽从许多岛屿上消失。物种丰富度下降，几乎所有岛屿上的功能和系统发育结构都变得聚类，这仅在统计上与地理和地形特征相关。岛屿上物种的分布变化与其在大陆的分布变化相关，这表明大陆群落动态通过海外定殖影响岛屿群落。尽管有物种定殖，但许多岛屿上物种丰富度的净损失、聚类的系统发育和功能结构以及顶级捕食者的消失表明该群岛的鸟类群落退化了。先前的研究表明，引入的鼬类通过争夺食物资源和对引入岛屿上的鸟类进行直接捕食而对鸟类产生负面影响。这些因引入鼬类而退化的鸟类群落可能会通过鸟类的岛间移动对整个群岛的群落产生跨界生物多样性影响，这表明需要在整个群岛采取全面的保护策略，以有效地保护岛屿生物多样性。
