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Formation of Species

Formation of Species. Section 3. The Concept of Species. Speciation – species formation. Existing species are changed versions of older species. Morphological Concept of Species. Morphology – internal and external structure and appearance of an organism. CONCEPT:

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Formation of Species

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  1. Formation of Species Section 3

  2. The Concept of Species • Speciation – species formation. • Existing species are changed versions of older species.

  3. Morphological Concept of Species • Morphology – internal and external structure and appearance of an organism. CONCEPT: • Species is defined according to their morphology. PROBLEM: -phenotype differences among species.

  4. Biological Species Concept • Proposed by Ernst Mayer 1904 • A species is a population of organisms that can interbreed and produce healthy offspring. • They cannot breed with other species.

  5. Isolating Mechanisms • Speciation begins with isolation.

  6. Geographic Isolation • Physical separation of members of a population • Ex. Deep canyon, river, crying climate in a valley • When the subpopulations become isolated, gene flow between them stops. • Natural selection and genetic drift cause the two subpopulations to diverge, eventually making them incompatible for mating. (2 new species)

  7. Example • Pupfish • Death valley has many ponds. • Each pond has a different species of fish that lives only in that pond. • Why did this happen? The valley was covered by a lake during the last ice age. • The ponds formed when the ice age ended. • Fish species became isolated and the environments of each pond differed enough that the separate populations of fish diverged.

  8. Reproductive Isolation • Results from barriers to successful breeding between population groups in the same area. Two types of Reproductive Isolation: • Prezygoticisolation- occurs before fertilization • Postzygoticisolation- occurs after fertilization.

  9. Prezygotic Isolation • Mating calls that are not recognized by the mate. • Difference in mating seasons. • Mechanical Isolation – difference in anatomy not allowing them to mate. • Ex. Wood frog and leopard frog, mating calls and mating times differ so they do not mate in the wild. • They do mate in captivity.

  10. Postzygotic Isolation • Offspring our not healthy (sterile). • Zygote dies after fertilization. • Offspring die quickly.

  11. Rates of Speciation • Speciation sometimes requires millions of years but some can form more rapidly. • Punctuatedequilibrium – sudden shift or change; species arise quickly or die quickly.

  12. Homework • Pg. 312 • 1-6

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