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SpeciationSpecies: A group of organisms capable of
interbreeding= they are isolated reproductively from other
species 1) Live together but cannot interbreed2) Live a distance apart
Isolating MechanismsPrezygotic isolating mechanisms: Barriers that
are in place before fertilization can occur. Eg. A mountain range between two populationsEg 2) Red clawed crab
Isolating MechanismsPrezygotic isolating mechanisms: Barriers that are in
place before fertilization can occur. Eg. A mountain range between two populations
Postzygotic isolating mechanism: Barriers that are in place after fertilization which prevent the production of fertile offspring
Eg. 1) Sperm and egg come together but the sperm is not able to enter the egg
Eg. 2) Offspring are produced but are infertile (mules)
Reproductive Isolating MechanismsPrezygotic Isolations
Definition Example
Habitat Isolation
Two species that live in the same location but in different habitats
One species may live in the trees one on the
forest floor
Reproductive Isolating MechanismsPrezygotic Isolations
Definition Example
Habitat Isolation
Two species that live in the same location but in different habitats
One species may live in the trees one on the
forest floor
Temporal Isolation
Two species have different breeding seasons. Individuals
become fertile at different times.
One flower may produce reproductive structures in
May another in August
Reproductive Isolating MechanismsPrezygotic Isolations
Definition Example
Habitat Isolation
Two species that live in the same location but in different habitats
One species may live in the trees one on the
forest floor
Temporal Isolation
Two species have different breeding seasons. Individuals
become fertile at different times.
One flower may produce reproductive structures in
May another in August
Behavioral Isolation
Animals have specific mating dances, calls and pheromones
A female peacock will only breed with a male who
can put on a good display
Reproductive Isolating MechanismsPrezygotic Isolations
Definition Example
Habitat Isolation
Two species that live in the same location but in different habitats
One species may live in the trees one on the
forest floor
Temporal Isolation
Two species have different breeding seasons. Individuals
become fertile at different times.
One flower may produce reproductive structures in
May another in August
Behavioral Isolation
Animals have specific mating dances, calls and pheromones
A female peacock will only breed with a male who
can put on a good display
Mechanical Isolation
Two species are not capable of mating
Genitalia does not match up
Reproductive Isolating MechanismPostzygotic Definition Example
Gamete Isolation
Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot
make it
Reproductive Isolating MechanismPostzygotic Definition Example
Gamete Isolation
Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot
make itZygote
IsolationFertilization occurs but zygote
cannot surviveFetus does not develop properly
and dies
Reproductive Isolating MechanismPostzygotic Definition Example
Gamete Isolation
Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot
make itZygote
IsolationFertilization occurs but zygote
cannot surviveFetus does not develop properly
and dies
Hybrid Sterility Hybrid survives but cannot produce its own offspring
Two species mate to produce an offspring that is sterile such as a
mule
Reproductive Isolating MechanismPostzygotic Definition Example
Gamete Isolation
Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot
make itZygote
IsolationFertilization occurs but zygote
cannot surviveFetus does not develop properly
and dies
Hybrid Sterility Hybrid survives but cannot produce its own offspring
Two species mate to produce an offspring that is sterile such as a
mule
F2 Fitness Hybrid can reproduce but their offspring cannot
The offspring of 2 species is able to reproduce but their offspring
can’t
The Process of Speciation
Speciation: When one species divided into two different species. Usually by mutation.
Allopatric Speciation: Geographic barriers such as rivers or mountain ranges divide a population. This prevents gene flow between the populations. Overtime the two populations develop into different species.
Sympatric Speciation
Sympatric Speciation: A new species is created within a population without the presence of geographical barriers.
Eg.
Sympatric Speciation
Sympatric Speciation: A new species is created within a population without the presence of geographical barriers.
Eg. One organism in a population of plants loses a chromosome. Because the chromosomes do not line up with its own species it can only reproduce with itself. Eventually it creates its own population of interbreeding plants.
Pace of Speciation
2 Hypothesis that address the pace of speciation
1) Phyletic Gradualism Model: Slow and steady change from one species to another.
Pace of Speciation
2) Punctuated Equilibrium: Long periods of no change are followed by short periods of rapid change
Fossil RecordsHow do Both Models Explain the lack of Transition Fossils in
the Fossil Record?Phyletic Gradualism: The change from one species to
another is the result of reproductive isolation (RI). RI cannot be seen in the fossil record so we can’t tell if two similar organisms are able to reproduce. Therefore we cannot tell if they are different species?
Punctuated Equilibrium: Because the new species forms suddenly there are few individuals that show the transition from the old species to the new species