Hanly Patrick J, Mittelbach Gary G, Schemske Douglas W
Am Nat. 2017 Jun;189(6):604-615. doi: 10.1086/691535. Epub 2017 Apr 7.
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.
自早期自然历史探险家发现物种丰富度从极地向赤道增加（纬度多样性梯度[LDG]）这一近乎普遍的模式以来，它一直备受关注。在众多为解释LDG而提出的假说中，（1）生产力、（2）可用于物种分化的时间和面积以及（3）物种形成和/或灭绝速率的纬度变化最近受到了最多关注。由于热带地区形成时间更早且以前分布更广，这些因素常常相互交织，阻碍了区分它们对LDG相对贡献的努力。在这里，我们研究了特有湖泊鱼类的全球分布，以确定湖泊年龄、面积和纬度如何分别影响物种形成的概率以及湖泊内发生的分化程度。我们分析了全球特有鱼类的分布（来自2746个湖泊中47个科的1933个物种和亚种），发现湖泊中含有特有物种的概率以及每个湖泊特有物种的总数随湖泊年龄和面积增加而增加，随纬度降低而减少。此外，在41个科中的34个科里，特有物种的地理位置比非特有物种的地理位置纬度更低。我们认为，低纬度地区鱼类的更大分化可能部分是由热带气候促进的生态机会以及物种相互作用的共同进化驱动的。
