Data from: Extinction-driven changes in frugivore communities on oceanic islands

Global change and human expansion have resulted in many species extinctions worldwide, but the geographic variation and determinants of extinction risk in particular guilds still remain little explored. Here, we quantified insular extinctions of frugivorous vertebrates (including birds, mammals and reptiles) across 74 tropical and subtropical oceanic islands within 20 archipelagos worldwide and investigated extinction in relation to island characteristics (island area, isolation, elevation and climate) and species’ functional traits (body mass, diet and ability to fly). Out of the 74 islands, 33 islands (45%) have records of frugivore extinctions, with one third (mean: 34%, range: 2–100%) of the pre-extinction frugivore community being lost. Geographic areas with more than 50% loss of pre-extinction species richness include islands in the Pacific (within Hawaii, Cook Islands and Tonga Islands) and the Indian Ocean (Mascarenes, Seychelles). The proportion of species richness lost from original pre-extinction communities is highest on small and isolated islands, increases with island elevation, but is unrelated to temperature or precipitation. Large and flightless species had higher extinction probability than small or volant species. Across islands with extinction events, a pronounced downsizing of the frugivore community is observed, with a strong extinction-driven reduction of mean body mass (mean: 37%, range: -18–100%) and maximum body mass (mean: 51%, range: 0–100%). The results document a substantial trophic downgrading of frugivore communities on oceanic islands worldwide, with a non-random pattern in relation to geography, island characteristics and species’ functional traits. This implies severe consequences for ecosystem processes that depend on mutualistic plant-animal interactions, including ecosystem dynamics that result from the dispersal of large-seeded plants by large-bodied frugivores. We suggest that targeted conservation and rewilding efforts on islands are needed to halt the defaunation of large and non-volant seed dispersers and to restore frugivore communities and key ecological interactions.全球变化与人类扩张已引发全球范围内的大规模物种灭绝，但针对特定功能群（guild）的灭绝风险地理变异及其驱动因素的研究仍较为匮乏。本研究对全球20个群岛内74个热带、亚热带海洋岛屿上的食果脊椎动物（涵盖鸟类、哺乳类与爬行类）的岛屿灭绝事件进行了量化分析，并探讨了灭绝事件与岛屿特征（岛屿面积、隔离度、海拔及气候）及物种功能性状（体重、食性与飞行能力）之间的关联。在74个研究岛屿中，33个（占比45%）存在食果动物灭绝记录，其灭绝前的食果动物群落平均有34%（范围：2%~100%）消失。物种丰富度较灭绝前下降超50%的区域包括太平洋的夏威夷群岛、库克群岛与汤加群岛，以及印度洋的马斯克林群岛与塞舌尔群岛。灭绝前群落的物种丰富度损失率在小型且隔离度高的岛屿上最高，随岛屿海拔升高而上升，但与温度或降水量无显著相关性。体型较大且无法飞行的物种，其灭绝概率显著高于体型较小或具备飞行能力的物种。在发生过灭绝事件的岛屿中，食果动物群落呈现出显著的体型小型化特征：受灭绝事件驱动，群落平均体重下降37%（范围：-18%~100%），最大体重下降51%（范围：0~100%）。本研究结果显示，全球海洋岛屿上的食果动物群落已出现显著的营养级降级现象，且其分布模式与地理区域、岛屿特征及物种功能性状均呈现非随机性关联。这对依赖动植物互利互作的生态系统过程造成了严重影响，其中包括由大型食果动物传播大种子植物所驱动的生态系统动态。我们建议，需针对岛屿开展针对性的保护与再野化（rewilding）工作，以遏制大型且无飞行能力的种子传播者的动物区系丧失，并恢复食果动物群落与关键生态互作关系。