Formation of Species Section 3. The Concept of Species Speciation – species formation. Existing...
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Transcript of Formation of Species Section 3. The Concept of Species Speciation – species formation. Existing...
![Page 1: Formation of Species Section 3. The Concept of Species Speciation – species formation. Existing species are changed versions of older species.](https://reader036.fdocuments.net/reader036/viewer/2022062314/56649e745503460f94b745c0/html5/thumbnails/1.jpg)
Formation of Species
Section 3
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The Concept of Species
• Speciation – species formation.
• Existing species are changed versions of older species.
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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 amongspecies.
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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.
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Isolating Mechanisms
• Speciation begins with isolation.
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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)
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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.
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Reproductive Isolation
• Results from barriers to successful breeding between population groups in the same area.
Two types of Reproductive Isolation:1. Prezygotic isolation- occurs before
fertilization2. Postzygotic isolation- occurs after
fertilization.
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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.
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Postzygotic Isolation
• Offspring our not healthy (sterile).
• Zygote dies after fertilization.
• Offspring die quickly.
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Rates of Speciation
• Speciation sometimes requires millions of years but some can form more rapidly.
• Punctuated equilibrium – sudden shift or change; species arise quickly or die quickly.
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• Homework• Pg. 312• 1-6
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