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模式（即纬度多样性梯度，latitudinal diversity gradient, LDG）自早期自然史探索者发现以来，一直是学界高度关注的研究课题。迄今已有诸多假说被提出以解释该纬度多样性梯度，其中近年受关注度最高的三类假说分别为：(1) 生产力的纬度差异；(2) 物种分化可用时间与面积的纬度差异；(3) 物种形成及/或灭绝速率的纬度差异。由于热带区域地质年代更久远且曾分布范围更广，上述因素往往相互交织，这使得厘清它们对纬度多样性梯度的相对贡献颇具难度。本研究聚焦内陆湖泊特有鱼类的全球分布格局，旨在探究湖泊年龄、面积与纬度各自如何影响湖泊内物种形成概率及物种分化程度。我们分析了全球范围内特有鱼类的分布数据（涵盖2746个湖泊中的47科、1933种及亚种），结果显示：湖泊拥有特有物种的概率及单湖特有物种总数，均随湖泊年龄与面积的增大而提升，随纬度升高而降低。此外，41个鱼类科中有34科的特有物种分布纬度显著低于非特有物种的分布纬度。我们提出，低纬度区域鱼类物种分化程度更高，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。