(Table S1) Diatom species richness from the Early Pleistocene to present

The extent to which the spatial distribution of marine planktonic microbes is controlled by local environmental selection or dispersal is poorly understood. Our ability to separate the effects of these two biogeographic controls is limited by the enormous environmental variability both in space and through time. To circumvent this limitation, we analyzed fossil diatom assemblages over the past ~1.5 million years from the world oceans and show that these eukaryotic microbes are not limited by dispersal. The lack of dispersal limitation in marine diatoms suggests that the biodiversity at the microbial level fundamentally differs from that of macroscopic animals and plants for which geographic isolation is a common component of speciation.

目前学界对海洋浮游微生物（marine planktonic microbes）的空间分布在多大程度上受局域环境选择或扩散作用调控这一问题，仍缺乏清晰认知。我们区分这两类生物地理调控因子效应的能力，受限于时空尺度下巨大的环境变异性。为规避这一局限，我们分析了全球海洋过去约150万年的化石硅藻组合（fossil diatom assemblages），并证实这类真核微生物（eukaryotic microbes）并不受扩散限制。海洋硅藻不存在扩散限制的现象表明，微生物层面的生物多样性本质上有别于大型动植物——地理隔离是后者物种形成过程中的常见诱因。