SpeciationSpeciation

Biology 10Biology 10at GIat GI

Biology 11Biology 11

SpeciationSpeciationThe development of a new species

Usually the result of reproductive isolation

How does this occur?

•Two populations of the same species are separated somehow•Separation may be by:

•Geography (geographical isolation)•Time (temporal isolation)•Behaviour (behavioural isolation)•Habitat (ecological isolation)

Separation leads to reproductive isolation

i.e. the members of the separate groups can no longer mate with members of the wider population

The now separate populations evolve in their own environments and in timeTheir gene pools will change independently of each other

With enough changes, interbreeding will no longer be possible

A NEW species is formed!

Modeling speciation in fruit fliesModeling speciation in fruit flies

Reproductive isolationReproductive isolation Physical barriers to reproduction result in Physical barriers to reproduction result in

ALLOPATRIC speciationALLOPATRIC speciation

Each environment is different allowing

for different adaptations to

become common

Three similar birds… on three different continents!(An example of geographical isolation)

Separation of beetle populations by a river

What about these two species?What about these two species?

The giant panda and the red panda live in the same habitat.

How did they speciate from a common ancestor?

Barriers to reproduction other than physical Barriers to reproduction other than physical (e.g. ecological, temporal, behavioural) lead (e.g. ecological, temporal, behavioural) lead to SYMPATRIC speciationto SYMPATRIC speciation

BIOLOGICAL DISTANCE – is a measure of the differences that exist between gene pools.

The greater (longer) the biological distance, the greater the difference between two species.

DIVERGENT EVOLUTIONDIVERGENT EVOLUTION

Diversification from simple to complex forms

e.g. complexity of shell leading to lighter, but stronger, shells. 

Divergent Evolution/Adaptive radiationDivergent Evolution/Adaptive radiation

Evidence for this is seen in fossil records

The number of similarities between populations of species decrease over time and hundreds or thousands of generations

Species from a common ancestor may grow to be completely dissimilar.

Happens because each species is subjected to different selection pressures

ADAPTIVE RADIATION:ADAPTIVE RADIATION:a special kind of divergent evolutiona special kind of divergent evolution

These organisms have similar but different beaks. These are homologous structures.

Adaptive Adaptive radiation radiation

beginning?beginning?

EXAMPLES OF CONVERGENT EXAMPLES OF CONVERGENT EVOLUTIONEVOLUTION

Convergent Evolution

Species from different evolutionarybranches come to resemble one another

Usually occurs between species in similar environments and therefore subjected to

similar selection pressures.

Results in body structures or even whole organisms that look similar

Similarity as a result of convergence is called analogy and such structures are called analogous structures

The two processes may work The two processes may work together:together:

How quickly does evolution How quickly does evolution occur?occur?

Gradualism Gradualism the theory that new species the theory that new species arise from many small changes building up arise from many small changes building up over timeover time

Gradually we see new species…Gradually we see new species…

The Role of ExtinctionThe Role of ExtinctionExtinction of a species means that the species was no longer ‘fit’ for survival.

It reproduces less than others, or not at all and its genes are not seen in future generations.

Few environmental changes few extinctions.

Large environmental changes (e.g. earthquake, climate change) many extinctions.

EXTINCTIONS OVER TIMEEXTINCTIONS OVER TIME

Theory of Punctuated EquilibriumTheory of Punctuated Equilibrium

If there are huge environmental changes, If there are huge environmental changes, many niches are left open via extinction and many niches are left open via extinction and some traits are highly “favoured” (passed on some traits are highly “favoured” (passed on more)more)

Speciation may occur more quickly Speciation may occur more quickly

Theory developed by Stephen Jay Gould Theory developed by Stephen Jay Gould and Niles Eldridge in 1972 and Niles Eldridge in 1972

Which do you think is more likely?Which do you think is more likely?