Speciation
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Speciation. What’s a species ? A group of organisms that normally interbreed in nature to produce fertile offspring What’s speciation ? The formation of a new species How does speciation happen?. Step 1- Geographic isolation A population of a species becomes physically separated

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Speciation

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Speciation

Speciation

What’s a species?

A group of organisms that normally interbreed in nature to produce fertile offspring

What’s speciation?

The formation of a new species

How does speciation happen?...


Speciation

Step 1- Geographic isolation

A population of a species becomes physically separated

(E.g. by a lake or mountain).


Speciation

Step 2- Natural selection

Each population changes over many generations through natural selection and mutation.

This results in subspecies populations that have their own different characteristics but can still interbreed.


Speciation

Step 3- Reproductive isolation

The populations change sufficiently for them to no longer be able to interbreed.

->A new species has been produced (speciation).


What changes might cause reproductive isolation

What changes might cause reproductive isolation?

  • Change in colour patterns

  • Change in mating habits

  • Seasonal differences in mating times

  • Changed chromosome that prevents sperm of one group from fertilising eggs of another

mates no longer recognised


Types of evolution

Types of evolution

  • Speciation shows us how new species might arise from a common ancestor.

  • Different evolutionary paths have been suggested:

    • Divergent evolution

    • Convergent evolution

    • Parallel evolution


Divergent evolution

Divergent evolution

  • Divergent evolution is when new forms of a species evolve from a common ancestor

    E.g. The Galapagos Island finches or the geographically isolated rabbits

  • Results in phenomenon known as adaptive radiation where ancestral organisms become adapted to their new environment and evolve into new forms suited to the environment

  • Figure 3.2.8 What environment would have resulted in the whale? The bat?


Convergent evolution

Convergent evolution

  • Convergent evolution or convergence occurs when organisms evolve and develop similar adaptations due to:

    • Living in similar environments and habitats

    • Having similar lifestyles and food source

    • Similar habitats -> similar characteristics selected for -> organisms that look similar despite having very different genes passed down from very different ancestors

    • These organisms may have analogous structures, specific body parts that are similar looking.

    • Figure 3.2.10


Parallel evolution

Parallel evolution

  • Parallel evolution occurs where related species evolve similar features while separated from each other

  • E.g. Old World monkeys and New World monkeys share many features because of their common ancestors, apart from their very different tails


To summarise

To summarise

  • Divergent = common ancestry, different environments, different organisms

  • Convergent = no common ancestry, similar environments, similar organisms

  • Parallel = common ancestry, different environments, similar organisms


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