Data from: Asymmetric geographic range expansion explains the latitudinal diversity gradients of four major taxa of marine plankton

Extensive investigation of the close association between biological diversity and environmental temperature has not yet yielded a generally accepted, empirically validated mechanism to explain latitudinal gradients of species diversity, which are common among taxa. Using the highly-resolved fossil records of four major taxa of marine plankton, we show that their gradients arise as a consequence of asymmetric geographic range expansion, rather than latitudinal variation in diversification rate, as commonly believed. Neither per-capita speciation nor extinction rates trend significantly with temperature or latitude for these marine plankton. Species of planktonic foraminifera and calcareous nannoplankton that originate in the temperate zone preferentially spread toward, and arrive earlier in the tropics to produce a normal gradient with tropical diversity peaks; by contrast, temperate-zone originating species of diatoms and radiolarians preferentially spread toward, and arrive earlier in polar regions to produce reversed gradients with high-latitude diversity peaks. Our results suggest that temperature affects latitudinal diversity gradients chiefly by its effect on species’ range limits rather than on probabilities of speciation and extinction. We show that this mechanism also appears to operate in various multicellular taxa, thus providing a widely applicable explanation for the origin of latitudinal diversity gradients.学界针对生物多样性与环境温度间紧密关联所开展的大量研究，迄今仍未得到一套被广泛认可且经实证验证的机制，用以解释在众多类群（taxa）中普遍存在的物种多样性纬度梯度格局（latitudinal gradients of species diversity）。本研究依托四大类海洋浮游生物（marine plankton）的高分辨率化石记录，证实其纬度梯度格局实为不对称地理范围扩张的产物，而非学界此前普遍认定的、分化速率随纬度变化所引发的结果。对于这些海洋浮游生物而言，其单位个体的物种形成速率与灭绝速率，均未随温度或纬度呈现显著的变化趋势。起源于温带的浮游有孔虫（planktonic foraminifera）与钙质超微浮游生物（calcareous nannoplankton）类群，会优先向热带海域扩散并更早抵达，由此形成以热带多样性为峰值的正向纬度梯度格局；与之相反，起源于温带的硅藻（diatoms）与放射虫（radiolarians）类群，则优先向极地海域扩散并更早抵达，由此形成以高纬度多样性为峰值的反向纬度梯度格局。本研究结果显示，温度对纬度多样性梯度格局的影响，主要是通过作用于物种的分布范围极限，而非改变物种形成与灭绝的概率。本研究还证实，该机制似乎同样适用于各类多细胞生物类群，从而为纬度多样性梯度格局的成因提供了普适性解释。