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导致全球范围内大量物种灭绝，但针对特定功能群（guild）的灭绝风险地理变异及其驱动因素，目前仍鲜有研究。本研究对全球20个群岛内74个热带与亚热带大洋岛屿上的食果脊椎动物（frugivorous vertebrates，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，并探究了灭绝事件与岛屿特征（岛屿面积、隔离度、海拔与气候）以及物种功能性状（体重、食性与飞行能力）之间的关联。在这74个岛屿中，33个（占比45%）存在食果脊椎动物灭绝记录，灭绝前的食果动物群落平均有34%（范围：2%~100%）的类群消失。物种丰富度损失超过50%的区域包括太平洋群岛（夏威夷群岛、库克群岛与汤加群岛境内）及印度洋群岛（马斯克林群岛、塞舌尔群岛）。原始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中最高，随岛屿海拔升高而上升，但与气温或降水量无显著关联。体型较大且无法飞行的物种，其灭绝概率高于小型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：由灭绝事件驱动的平均体重（平均下降37%，范围：-18%~100%）与最大体重（平均下降51%，范围：0~100%）均大幅降低。本研究结果表明，全球大洋岛屿上的食果动物群落正经历显著的营养级降级，且这种变化呈现出与地理格局、岛屿特征及物种功能性状相关的非随机模式。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。