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 location of endemics in 34 of 41 families are found at lower latitudes than that of non-endemics. 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这一近乎普适的格局（纬度多样性梯度，latitudinal diversity gradient, LDG），自早期自然史探险家发现以来便一直受到学界的高度关注。在诸多用以解释该纬度多样性梯度的假说中，近年来受关注最多的三类分别为：1）生产力的纬度差异，2）物种分化可用的时间与面积，3）物种形成及/或灭绝速率的纬度变化。由于热带区域历史更为悠久且昔日分布范围更广，上述三类因素往往相互交织，使得厘清它们对纬度多样性梯度的相对贡献颇具难度。本研究通过分析淡水湖泊特有鱼类的全球分布格局，旨在探究湖泊年龄、面积与纬度分别如何影响湖泊内的物种形成概率及物种分化规模。我们对全球范围内的特有淡水鱼类分布进行了分析，涵盖2746个湖泊中的47科共1933个物种及亚种，结果发现：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加而上升，随纬度升高而下降。此外，41个鱼类科中有34个科的特有类群，其分布纬度均低于非特有类群。我们据此提出，低纬度区域鱼类物种分化程度更高，其部分驱动因素可能为热带气候所催生的生态机遇，以及物种间相互作用的协同进化。