Geographical gradients of vertebrate species richness are determined jointly by evolutionary and environmental factors. Support for these factors comes mostly from tetrapods and, recently, marine fishes, but their validity and relative importance in freshwater fishes is not well understood. Here, we describe the species richness gradient for the major component of the viviparous freshwater fishes of the Americas, the poeciliids, and test the effects of evolutionary and environmental factors on this pattern.

中文翻译：

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美洲坡尾鱼类物种丰富度的进化和环境驱动因素

脊椎动物物种丰富度的地理梯度是由进化和环境因素共同决定的。对这些因素的支持主要来自四足动物和近来的海水鱼类，但对于它们在淡水鱼类中的有效性和相对重要性尚不甚了解。在这里，我们描述了美洲的活生胎的淡水鱼的主要组成部分的物种丰富度梯度，即poeciliids，并测试了进化和环境因素对该模式的影响。