Diversification & Extinctions

Macroevolution = Big Time Change! Changes occur to species to various degrees in response to environmental changes – they may be drastic or hardly noticeable. Changes occur to species to various degrees in 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. 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. 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 cell being formed from the “primordial soup” of a very young earth. Last time…We left off with an early prokaryotic 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. 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. 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 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. Eukaryotes may have begun to develop from 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. 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. 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. 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 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. A symbiotic relationship would have developed – energy 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 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. 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?... 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. 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. 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. Archaebacteria gave rise to methanogens, thermophiles and halophiles. Eubacteria were aerobic and others were autotrophic (photosynthetic). 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. 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. 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. 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? 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 species that are capable of coping in the new environment. They have been naturally selected and are seen as fit to continue. Not everyone is killed – there are surviving 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! 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! 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 (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! If you need to switch to a new resource (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. 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. 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. 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. 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 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. 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??? 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. 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…

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