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Chapter 19 Speciation

Chapter 19 Speciation - Chapter 19 Speciation and...

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Chapter 19 Speciation and Macroevolution
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So what is a species? Species are groups of populations that  have evolved independently. 7 - 10 million species. Biodiversity  is the total range of species  diversity.
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Biological Species Concept Species are groups of populations  that do, or can interbreed in nature Produce fertile offspring Each species gene pool is separate
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Limitations to Biological Species Concept 1. Does not help determine species of  asexually reproducing organisms. 2. It’s not always possible to observe if  two groups are interbreeding.
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So, how do new species form? Speciation , they way in which a new  species forms, depends on 2 factors: 1. The isolation of populations 2. Genetic divergence of populations.
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Prevent gene flow between species Prezygotic barriers Prevent mating or fertilization Postzygotic barriers Reproductive failure after fertilization Reproductive isolating mechanisms
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Premating Isolating Mechanisms Temporal isolation Habitat isolation Behavioral isolation Mechanical isolation Gametic isolation
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Temporal  isolation Mating at  different times  of year Mating at  different times  of day
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Habitat isolation Different habitats in the same area Gametic isolation Incompatible egg and sperm Molecular recognition on the surface of  the cells
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Behavioral (sexual) isolation Required courtship behaviors
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Mechanical isolation Incompatible genital organs Only small bees can land on the petal of the black sage Only large bees brush against the stamens of the white sage
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Hybrid inviability hybrid embryos die when genetic regulation  fails during development Hybrid sterility problems during meiosis cause abnormal  gametes Hybrid breakdown The progeny of the hybrid individuals are  sterile. Postzygotic barriers
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Speciation The evolution of a new species. Occurs when a population becomes  reproductively isolated from other  populations of the species.  Two main types of isolation Allopatric Speciation Sympatric Speciation
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Geographically separated populations Most common form of speciation in  animals Genetic drift in small populations Allopatric speciation
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Squirrel species separated by the Grand Canyon have diverged in fur color
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