Sato Nozomu, Nakashita Rumiko, Sasaki Tetsuro, Kato Hidetoshi, Karube Haruki, Mori Hideaki, Kawakami Kazuto
Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo, 192-0397, Japan.
Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan.
Oecologia. 2025 May 22;207(6):88. doi: 10.1007/s00442-025-05725-0.
Seabirds are responsible for transporting marine material to oceanic islands, and attempts are being made to restore their function on many islands where they have become extinct. However, little is known about the original island ecosystems prior to disturbance. Minamiiwoto, located in the Ogasawara Islands, is an uninhabited oceanic island that remains uninvaded by alien animals, and its pristine ecosystem and material cycle should serve as a reference for the restoration of disturbed island ecosystems. We analyzed the food web structure of several of the Ogasawara Islands with different disturbance intensities using stable isotopes (δC, δN) and compared the characteristics of the material cycle. We found that seabirds and land crabs are distributed across the entire island of Minamiiwoto, with high δN values derived from marine resources and a gradient in the δN of land crabs reflecting differences in seabird species with elevation. In contrast, on islands where forest-nesting seabirds have been extinct for more than 50 years, the nutrient supply to the island interior has been lost, and the δN of most organisms was significantly lower. Isotopic food niches among predators were clearly partitioned by species (max. 14% overlap) on Minamiiwoto, while on the disturbed islands they tended to be highly similar (max. 53% overlap). Our results confirmed that Minamiiwoto still maintains a pristine ecosystem characterized by material transport by seabirds and decomposition by land crabs. The recovery of these biological functions should be the guide for conservation and restoration of oceanic islands subjected to anthropogenic disturbance.
海鸟负责将海洋物质输送到海洋岛屿，并且人们正在努力恢复它们在许多海鸟已经灭绝的岛屿上的功能。然而，对于受到干扰之前的原始岛屿生态系统，我们知之甚少。位于小笠原群岛的南伊豆岛是一座无人居住的海洋岛屿，尚未受到外来动物的侵扰，其原始生态系统和物质循环应可作为受干扰岛屿生态系统恢复的参考。我们使用稳定同位素（δC、δN）分析了小笠原群岛中几个具有不同干扰强度的岛屿的食物网结构，并比较了物质循环的特征。我们发现，海鸟和陆地蟹分布在南伊豆岛全岛，其高δN值源自海洋资源，陆地蟹的δN值随海拔变化，反映了海鸟种类的差异。相比之下，在森林筑巢海鸟已经灭绝超过50年的岛屿上，岛屿内部的养分供应已经丧失，大多数生物的δN值显著降低。在南伊豆岛，捕食者之间的同位素食物生态位按物种明显划分（最大重叠率为14%），而在受干扰的岛屿上，它们往往高度相似（最大重叠率为53%）。我们的结果证实，南伊豆岛仍然保持着以海鸟物质运输和陆地蟹分解为特征的原始生态系统。恢复这些生物功能应成为受人为干扰的海洋岛屿保护和恢复的指导原则。
