Approximately 1/3 of all species of fish live in freshwater, the other 2/3 are saltwater species. However, freshwater lakes and rivers cover only about 1% of the Earths surface, compared to salt water, which covers 3/4 of the Earths surface. Which of the following arguments might best explain the diversity of freshwater fishes in this spatially limited habitat? ?

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    Freshwater fishes have undergone a series of evolutionary bottlenecks (bottleneck effect).
    Freshwater fishes have lower overall genetic variability, resulting in increased chances for extinction.
    There are greater opportunities for separation of populations in freshwater habitats, which has led to higher levels of allopatric speciation.
    Freshwater fishes are probably subject to higher mutation rates than saltwater species.
asked May 19, 2013 in Biology by anonymous
    

1 Answer

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There are greater opportunities for separation of populations in freshwater habitats, which has led to higher levels of allopatric speciation.
answered May 20, 2013 by Bioshare ~Top Expert~ (34,070 points)

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