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Chapter 23

Chapter 23


Department
Biological Sciences
Course Code
BIOA02H3
Professor
Kamini Persaud
Chapter
23

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Sanchika Kanagalingam
April 1st 2011
Biology II
Chapter 23: Species and their
Formation
What are species?
Speciation- the process by which one species splits into two or more daughter species.
Speciation occurs gradually over a long period of time
Species- kind defined in different ways
Morphological Species Concept
Classify them differently by how they look
Darwin was one of the people who used this concept
Members would look alike because they share alleles
Binomial system of nomenclature- every species have a genus
onot good enough
oeg.female- this is a new species
male- this is a different species because they dont look alike
odifferent breeds of dogs dont not look the same but they can breed
Biological Species Concept: (Ernst Mayr)
classify species based on where they can produce viable offspring’s
two different species can also live together and cant reproduce
you can mate with individuals in your group but not ouside
some animals are morphologically distinct but are not biologically distinct
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Sanchika Kanagalingam
April 1st 2011
Biology II
Reproductive isolation: individuals in a population can mate with each other, but not
with those of another population.
How do species arise?
Not all evolutionary change results in new species, but species can become isolated into 2
populations
oIn each isolated gene pool, allele and genotype changes as a result of evolutionary
change
Have a species over time changes in response to its environment
oBut does not mean they cannot interbreed
oIf some individuals in a population gets isolated from other indiviiduals what
happens is evolution change does occur in both populations
If they cant interbreed the changes does not occur in both group but one
group it makes two different species
Allopatric Speciation
When populations are separated by a physical barrier (geographic speciation)
The dominant mode of speciation
oDue to continents drift, sea level changes
Environment- different populations evolve different
Populations evolve due to different environment
Can form different species if crossing a barrier and not being able to come back
oThey individually evolve
Eg. Darwins finches in each island
All looked different , evolved differently due to different pressure
in each island
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Sanchika Kanagalingam
April 1st 2011
Biology II
Eg. Porkfish
oUsed to be one species (3 half million years ago )
oNorth America and south America two different continents and water between
them
oLand bridge formed from and both continents became one
Individuals on one side evolved amongst themselves and other side
evolved amongst themselves
oBoth individuals cant reproduce with each other
Making them two different species
Allopatric speciation can occur via Vicariant event and dispersal
Sympatric speciation
Does not require physical isolation
Ecological isolation
oPopulations of individuals live in one niche and other individuals and live in
another niche and they dont interbreed since they use other resources
oDisruptive selection
Become one kind or another individual not in between and breed with only
one
oEg. Apple maggot flies
Native to the area
Some flies deposit eggs on hawthorn fruits and some flies deposit eggs lay
eggs on apples
Hawthorn fruit flies only mate with hawthorn fruit flies and apple fruit
flies only mate with apple fruit flies making them ecologically isolated
Polyploidy
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