Ecology and Evolution

How does speciation occur?
Answered by Planet Green
  • Planet Green

    Planet Green

  1. According to evolutionists, there are four basic modes of speciation, or the splitting of a species into two distinct species. Speciation usually is caused by species being isolated from one another geographically or by some event that reduces the gene flow of a species.

    • Allopatric speciation occurs when a physical boundary like a mountain or a river separates a species. It's the scientific name for the geographic isolation that can cause a species to split. For example, 3 million years ago, the Isthmus of Panama formed, closing off the land between North America and Central America. Researchers from the Smithsonian Tropical Research Institute in Panama have studied how this change in geology affected the region's snapping shrimp population. Shrimp on either side of the isthmus were nearly identical, but when researchers tried to mate them, the shrimp wanted nothing to do with one another. In fact, the shrimp lived up to their names and snapped at their neighbors [source: PBS].
    • Parapatric speciation occurs when a species is so spread out over a large area that its different groups adapt to their home areas and eventually become distinct. It is a form of allopatric speciation that is caused by increasing gene flow between certain subpopulations of a species. This eventually causes the subspecies to be distinct from their original species. Researchers point to grasses located in contaminated soils that have adapted to survive in the high-metal environment near mines. Grasses of the same species are located nearby but in normal soil for the area. The grasses in the poor soil have begun to flower at different times so that the two types of plants can no longer reproduce; eventually there will be no gene flow between these plants from the same species.
    • Peripatric speciation also is a form of allopatric speciation that involves a small section of the population splitting off and becoming distinct; this often produces a genetic bottleneck. Limited numbers are critical to peripatric speciation.
    • Sympatric speciation also is a form of allopatric speciation that involves a small section of the population splitting off and becoming distinct; this often produces a genetic bottleneck. Limited numbers are critical to peripatric speciation.


    Evolve In Isolation 2
    Mountain ranges, like the Himalayas in Asia, are more than vast enough to foster allopatric speciation. (Prakash Mathema/AFP/Getty Images)

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