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分布模式——纬度多样性梯度（latitudinal diversity gradient, LDG）的起源与动态机制，长期以来的一项核心阻碍是：过往研究往往狭隘地仅聚焦单一因果因素，而当前亟需更具综合性、整合性的研究范式。本研究以海洋双壳类（marine bivalves）为模式系统，尽可能借鉴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维度的综述：其一认为纬度多样性梯度主要由（a）局域环境因素塑造——这类因素决定了特定纬度带的物种及高级分类单元数量（即原位假说（in-situ hypotheses)）；其二则主张梯度形成源于（b）由其他区域起源的演化谱系迁入焦点区域（即空间动态假说（spatial-dynamics hypotheses)）。支持原位假说的证据包括：多数演化支的现存多样性趋势与温度等环境因素的拟合程度，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的相关性。支持空间动态假说的证据则有：不同纬度带双壳类属的年龄-频率分布，该分布与‘走出热带’的动态模式相符；此外，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区域，同样印证了这一假说。由此可见，原位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梯度，且这两类过程很可能也作用于其他生物类群。尽管在呈现相似纬度多样性梯度的类群中，这两种过程的相对强度可能存在差异，但要精准解析其各自的效应，仍需开发将化石数据与分子系统发育相结合的改进方法。本研究还梳理了若干潜在的研究方向，并提出：诸多古今最显著的生物分布模式，大概率是由多样且相互强化的驱动因素共同促成的。