Data from: Speciation and the latitudinal diversity gradient: insights from the global distribution of endemic fish

The nearly universal pattern that species richness increases from the poles to the equator (the latitudinal diversity gradient [LDG]) has been of intense interest since its discovery by early natural-history explorers. Among the many hypotheses proposed to explain the LDG, latitudinal variation in (1) productivity, (2) time and area available for diversification, and (3) speciation and/or extinction rates have recently received the most attention. Because tropical regions are older and were formerly more widespread, these factors are often intertwined, hampering efforts to distinguish their relative contributions to the LDG. Here we examine the global distribution of endemic lake fishes to determine how lake age, area, and latitude each affect the probability of speciation and the extent of diversification occurring within a lake. We analyzed the distribution of endemic fishes worldwide (1,933 species and subspecies from 47 families in 2,746 lakes) and find that the probability of a lake containing an endemic species and the total number of endemics per lake increase with lake age and area and decrease with latitude. Moreover, the geographic locations of endemics in 34 of 41 families are found at lower latitudes than those of nonendemics. We propose that the greater diversification of fish at low latitudes may be driven in part by ecological opportunities promoted by tropical climates and by the coevolution of species interactions.

物种丰富度从极地向赤道递增的近乎普适分布模式——即纬度多样性梯度（latitudinal diversity gradient, LDG）——自早期自然史探险家发现以来，一直是学界广泛关注的核心议题。在诸多用以解释该纬度多样性梯度的假说中，近年来受到最多关注的三类分别为：(1) 生产力的纬度梯度变化；(2) 物种分化可利用的时间与空间面积；(3) 物种形成及/或灭绝速率的纬度差异。由于热带区域历史更为悠久且曾分布范围更广，上述因素往往相互交织，极大阻碍了学界厘清它们对纬度多样性梯度相对贡献的研究尝试。本研究以全球湖泊特有鱼类的分布为研究对象，旨在解析湖泊年龄、面积及纬度分别如何影响湖内物种形成概率与物种多样化程度。我们对全球范围内的特有鱼类分布开展了系统性分析（涵盖2746个湖泊中的47科，共计1933个物种及亚种），结果显示：湖泊包含特有物种的概率，以及单个湖泊的特有物种总数，均随湖泊年龄与面积的增加而升高，随纬度升高而降低。此外，在41个鱼类科中，有34个科的特有物种地理分布点位相较于非特有物种更偏向低纬度区域。我们提出，低纬度区域鱼类物种多样化程度更高这一现象，或许部分源于热带气候所催生的生态机遇，以及物种间相互作用的协同演化。