The number of fish taxa that occur exclusively in marine biomes is approximately equal to the number that occur in freshwater biomes. Both the geographic area and habitable volume of the marine realm are vastly greater than for Earth's freshwater ecosystems, suggesting that the density of marine species is proportionately much lower in the oceans. Because freshwater lineages are relatively recently derived from older marine lineages, this difference in species density suggests that speciation rates might be elevated in freshwater systems. I tested whether speciation rates differ systematically between freshwater and marine habitats.

中文翻译：

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淡水和海洋中鱼类的物种形成率和多样性

仅在海洋生物群落中发生的鱼类分类单元的数量大约等于在淡水生物群落中发生的鱼类分类单元的数量。海洋领域的地理区域和可居住量都大大大于地球的淡水生态系统，这表明海洋中海洋物种的密度相应地要低得多。由于淡水谱系是相对较新的源自较旧的海洋谱系，因此物种密度的这种差异表明，淡水系统的物种形成率可能会提高。我测试了淡水和海洋栖息地之间的物种形成率是否系统地不同。