Data from: Shaping the latitudinal diversity gradient: New perspectives from a synthesis of paleobiology and biogeography

An impediment to understanding the origin and dynamics of the latitudinal diversity gradient (LDG) -- the most pervasive large-scale biotic pattern on Earth -- has been the tendency to focus narrowly on a single causal factor, when a more synthetic, integrative approach is needed. Using marine bivalves as a model system, and drawing on other systems where possible, we review paleobiologic and biogeographic support for two supposedly opposing views, that the LDG is shaped primarily by (a) local environmental factors that determine the number of species and higher taxa at a given latitude (in-situ hypotheses), or (b) the entry of lineages arising elsewhere into a focal region (spatial-dynamics hypotheses). Support for (a) includes the fit of present-day diversity trends in many clades to environmental factors such as temperature, and the correlation of extinction intensities in Pliocene bivalve faunas with net regional temperature changes. Support for (b) includes the age-frequency distribution of bivalve genera across latitudes, which is consistent with an out-of-the-tropics dynamic, as are the higher species diversities in temperate southeast Australia and southern Japan than in the tropical Caribbean. Thus, both in-situ and spatial-dynamics processes must shape the bivalve LDG, and are likely to operate in other groups as well. The relative strengths of the two processes may differ among groups showing similar LDGs, but dissecting their effects will require improved methods of integrating fossil data with molecular phylogenies. We highlight several potential research directions, and argue that many of the most dramatic biotic patterns, past and present, are likely to have been generated by diverse, mutually reinforcing drivers.理解地球最普遍的大型生物地理格局——纬度多样性格局（latitudinal diversity gradient, LDG）的起源与动态，所面临的一大阻碍，便是过往研究往往仅狭隘地聚焦单一成因因素，而学界亟需更具综合性、整合性的研究路径。本研究以海洋双壳类作为模式类群，并尽可能参考其他类群的研究证据，对两种看似对立的观点展开古生物学与生物地理学层面的梳理与佐证：其一，纬度多样性格局主要由局域环境因素主导，此类因素决定了特定纬度带的物种与高阶类群数量（原地假说，in-situ hypotheses）；其二，纬度多样性格局由源自其他区域的演化支迁入焦点区域所驱动（空间动态假说，spatial-dynamics hypotheses）。支持原地假说的证据包括：诸多演化支的现代多样性格局与温度等环境因素高度契合，以及上新世海洋双壳类动物群的灭绝强度与区域净温度变化存在显著相关性。支持空间动态假说的证据包括：不同纬度带双壳类属的年龄-频率分布符合“走出热带”（out-of-the-tropics）的演化动态，澳大利亚东南部温带海域与日本南部海域的物种多样性高于热带加勒比海域的观测结果，同样印证了该假说。由此可见，原地过程与空间动态过程共同塑造了海洋双壳类的纬度多样性格局，且此类机制大概率也作用于其他生物类群。尽管对于呈现相似纬度多样性格局的不同类群而言，两种过程的相对作用强度可能存在差异，但要厘清二者的具体效应，亟需开发整合化石数据与分子系统发育的新型研究方法。本研究还梳理了若干潜在的研究方向，并提出：诸多过往与现存的典型生物地理格局，大概率是由多种相互协同的驱动因素共同塑造的。