Speciation
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Speciation. A species is an interbreeding group of organisms When a population is somehow severed from the parent population and over time its gene pool is altered. Allopatric and sympatric. Allopatric speciation. Isolation is the result of a geographic barrier Ex. Galapagos finches

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Speciation

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Speciation

Speciation

  • A species is an interbreeding group of organisms

  • When a population is somehow severed from the parent population and over time its gene pool is altered.

  • Allopatric and sympatric


Allopatric speciation

Allopatric speciation

  • Isolation is the result of a geographic barrier

  • Ex. Galapagos finches

  • True speciation only occurs if the remaining populations will NOT breed


Allopatric

allopatric


Sympatric speciation

Sympatric speciation

  • No geographic barrier

  • Balanced polymorphisms – insects a certain color with a certain kind of camoflage will mate and isolate themselves from the original population

  • Hybridization – when hybrids are more successful than parental generations


Sympatric polyploidy

Sympatric - polyploidy

  • When a sub-population arises in the midst of the parent population

  • Many plant species have accidental polyploidy in meiosis. They produce zygotes with multiple sets of chromosomes.

  • They can no longer reproduce with parental generation.


Evolution of wheat

Evolution of Wheat


Adaptive radiation

Adaptive Radiation

  • Adaptive radiation – rapid evolution of a variety of species from a single ancestor (ex. Darwin’s finches)

  • Occurs after mass extinctions when 90% of organisms become extinct. Leaves room for others to colonize


Adaptive radiation1

Adaptive Radiation


What is the tempo of speciation

What is the tempo of speciation?

  • Phyletic gradualism vs. punctuated

  • Punctuated equilibrium model – species most often diverge in spurts of rapid change instead of slow and gradually.

  • Over a few to ten thousand years, genetic drift and natural selection can change small, isolated species


Punctuated equilibrium

Punctuated Equilibrium


Reproductive barriers

Reproductive Barriers

  • Prezygotic barriers – occur before conception

  • Post-zygotic barriers – occurs after conception


Pre zygotic barriers

Pre-zygotic Barriers

  • Temporal Isolation – mating or flowering occur at different time of the year/day

    Ex. Western spotted skunks breed in fall, while eastern spotted skunks breed in the late winter

  • Habitat Isolation – species living in the same region may occupy different habitats

    Ex. Some Garter snakes live in water/some on land

  • Behavioral Isolation-courtshiprituals are very specific

    Ex. Birds

  • Mechanical isolation-structuraldifferences in genitalia or flowers prevent copulation or pollen transfer

    Ex. Insects and flowers

  • Gametic isolation- male sperm cannot fertilize the egg


Post zygotic barriers

Post-zygotic Barriers

  • Hybrid Inviability – hybrid zygotes fail to develop or reach sexual maturity

  • Hybrid Sterility – Hybrid individuals fail to produce young

  • Hybrid breakdown – hybrids have reduced viability with each generation.


Patterns of evolution

Patterns of Evolution

  • Divergent evolution – when two isolated population evolve independently (Ex. Brown and polar bears)

  • Convergent Evolution – when two organisms without a common ancestor occupy the same niche, so they have the same characteristics. (ex. Porpoise and penguin)

  • Parallel Evolution – two related species who have made similar evolutionary changes. Ex. Placental and marsupial wolf

  • Co-evolution – predator/prey relationships


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