Institute of Integrative Biology, ETH Zurich (Swiss Federal Institute of Technology), Zurich, Switzerland.
Department of Ecology and Evolutionary Biology, The University of Kansas, Lawrence, KS, USA.
Nature. 2024 Mar;627(8003):335-339. doi: 10.1038/s41586-024-07110-y. Epub 2024 Feb 28.
The latitudinal diversity gradient (LDG) dominates global patterns of diversity, but the factors that underlie the LDG remain elusive. Here we use a unique global dataset to show that vascular plants on oceanic islands exhibit a weakened LDG and explore potential mechanisms for this effect. Our results show that traditional physical drivers of island biogeography-namely area and isolation-contribute to the difference between island and mainland diversity at a given latitude (that is, the island species deficit), as smaller and more distant islands experience reduced colonization. However, plant species with mutualists are underrepresented on islands, and we find that this plant mutualism filter explains more variation in the island species deficit than abiotic factors. In particular, plant species that require animal pollinators or microbial mutualists such as arbuscular mycorrhizal fungi contribute disproportionately to the island species deficit near the Equator, with contributions decreasing with distance from the Equator. Plant mutualist filters on species richness are particularly strong at low absolute latitudes where mainland richness is highest, weakening the LDG of oceanic islands. These results provide empirical evidence that mutualisms, habitat heterogeneity and dispersal are key to the maintenance of high tropical plant diversity and mediate the biogeographic patterns of plant diversity on Earth.
纬度多样性梯度（LDG）主导着全球多样性模式，但构成 LDG 的因素仍难以捉摸。在这里，我们使用独特的全球数据集表明，海洋岛屿上的维管植物表现出减弱的 LDG，并探索了这种效应的潜在机制。我们的结果表明，岛屿生物地理学的传统物理驱动因素——即面积和隔离——有助于解释在给定纬度上岛屿和大陆多样性之间的差异（即岛屿物种赤字），因为较小和较远的岛屿经历了减少的殖民化。然而，与共生植物物种在岛屿上的代表性不足，我们发现这种植物共生过滤比生物因素更能解释岛屿物种赤字的更多变化。特别是，需要动物传粉者或微生物共生体（如丛枝菌根真菌）的植物物种不成比例地导致赤道附近岛屿的物种赤字增加，而随着与赤道的距离增加，其贡献减少。在大陆丰富度最高的低绝对纬度，植物共生过滤对物种丰富度的影响特别强烈，从而减弱了海洋岛屿的 LDG。这些结果提供了经验证据，表明共生关系、栖息地异质性和扩散是维持热带植物高多样性的关键，并调节了地球上植物多样性的生物地理模式。
