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 occur in most taxa. Using the highly resolved late Cenozoic 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.针对生物多样性与环境温度间紧密关联的大量系统性研究，迄今尚未形成一套被广泛认可且经实证验证的机制，用以解释多数类群（taxa）中普遍存在的物种多样性纬度梯度格局。本研究借助高分辨率的晚新生代海洋浮游生物四大类群化石记录，证实其纬度梯度格局并非如学界普遍认为的那样，源于多样化速率的纬度差异，而是不对称地理范围扩张的结果。对于这些海洋浮游生物而言，其单位物种形成速率与灭绝速率均未随温度或纬度呈现显著变化趋势。起源于温带的浮游有孔虫（planktonic foraminifera）与钙质超微浮游生物（calcareous nannoplankton）物种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；与之相反，起源于温带的硅藻（diatoms）与放射虫（radiolarians）物种则优先向极地海域扩散并更早抵达，进而形成以高纬度多样性为峰值的反向梯度。本研究结果表明，温度对纬度多样性梯度的影响主要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。我们还证实，这一机制在各类多细胞类群中同样适用，从而为纬度多样性梯度的起源提供了普适性解释。