Download Diversification & Extinctions

Diversification & Extinctions
Macroevolution = Big Time Change!
• Changes occur to species to various degrees in
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response to environmental changes – they may
be drastic or hardly noticeable.
Sometimes, these changes within species and
populations are significant enough to bring
about new groups within a taxon or new taxa
altogether.
When new groups or levels arise due to changes
in a population or species – we say it is a case of
macroevolution.
Endosymbiosis in Eukaryotic Cells
• Last time…We left off with an early prokaryotic
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cell being formed from the “primordial soup” of
a very young earth.
These early prokaryotes would have given rise
to the two modern bacterial kingdoms –
archaebacteria and eubacteria.
One would think us eukaryotes would have
arisen from the eubacterial lineage but this is
not so…We actually have more similarities to the
archaebacteria – the bacteria that today live in
the harshest areas on Earth.
Prokaryote  Eukaryote?
• Eukaryotes may have begun to develop from
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prokaryotes as the cell membrane may have
folded inward and formed the nucleus,
endoplasmic reticulum and vacuoles – all made
of a phospholipid bilayer. Thus we have the
beginnings of the first eukaryotic lineage.
Researchers believe that the process of
endosymbiosis accounts for the presence of
mitochondria and chloroplasts. This would
only add to the abilities of early eukaryotic cells.
Endosymbiosis?
• Mitochondria and chloroplasts may have
been engulfed by the early eukaryotes in a
process similar to phagocytosis. They
were seen as aerobic bacteria and
photosynthetic bacteria by the host cell
respectively.
• They would have been surrounded by a
vesicle made of the host cell’s
membrane. This would help to protect
them inside the cell.
Endosymbiosis?
• A symbiotic relationship would have developed – energy
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rich molecules (ATP) would have been supplied to the
host and the “invader” would have a nutrient-rich home
in which to live – it’s win-win baby! This is known as
mutualism.
The mitochondria and chloroplasts would have multiplied
quite rapidly in their new nutrient-rich surroundings.
The heterotrophic eukaryotes would have only taken
up the mitochondria while the autotrophic eukaryotes
would have taken up both the mitochondria and the
chloroplasts.
Show Me The Money!
• What evidence is there that this
endosymbiotic thing even happened?...
• They have two membranes – no other
organelles do. The two membranes differ
from one another based on their make-up.
• Both chloroplasts and mitochondria
replicate their own DNA which resembles
eubacterial DNA. This division is
independent of the host cell’s division.
Unicellular  Multicellular!
• Archaebacteria gave rise to methanogens,
thermophiles and halophiles.
• Eubacteria were aerobic and others were
autotrophic (photosynthetic).
• As more and more photosynthesis took
place the content of the atmosphere went
from one dominated by carbon dioxide to
one with a greater oxygen content.
Mass Extinction = Diversity?!?!
• Mass extinctions are events that
dramatically alter the environment and
lead to the death of an incredible number
of species in a large geographical area.
• After every mass extinction you see a
noticeable increase in the diversity of the
subsequent geological period.
• Why is this? How does a lot of death lead
to an abundance of life?
Mass Extinction = Diversity?!?!
Life After Death!!!
• Not everyone is killed – there are surviving
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species that are capable of coping in the new
environment. They have been naturally selected
and are seen as fit to continue.
These fit survivors now have whatever
resources are available to themselves with little
or no competition – life is good and numbers go
way up! This could be a source of competition!
The new environment has many unfilled
niches whose species have gone extinct – there
was a mass extinction after all!
Life After Death!!!
• If you need to switch to a new resource
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(because of intraspecific competition) or you
desire something that was previously unavailable
because you weren’t the best fit at attaining it –
well now you are in luck!
Nobody else is around so get it done! Go forth
and move into a new role.
Think – it’s like Darwin’s finches – move in from
South America as a single species and evolve
into many different species in the absence of
other birds.
The Rate of Evolution
• There are two main ideas – gradualism
and punctuated equilibrium.
• Gradualism states that evolution takes
place over long periods of time and that
changes accumulate slowly over this time.
• The environment is slow in changing and
so is the divergence within a species.
The Rate of Evolution
• Punctuated Equilibrium states that speciation
and change occurs in very short spurts and then
is followed by long periods of little or no
significant change.
• So who is the winner???
• They both are! With evidence (the fossil record)
being incomplete – you could not say which is
more accurate because there is evidence for
both theories at work.
Both Views Presented…
FIN