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Transcript
Types of
Natural Selection
Directional
Selection
• One extreme of a
specific trait is more
advantageous than both
the other extreme and
the average trait.
• It pays to be different!!
• Examples:
– Peppered Moth
– Bacteria that are
genetically resistant to
some antibiotics.
Video
http://www.pbs.o
rg/wgbh/evolutio
n/library/10/4/l_
104_03.html
Stabilizing
Selection
• Tends to eliminate
individuals on both
ends of the genetic
spectrum.
• It pays to be average!!
• Occurs when the
environment changes
little and most species
are well-adapted.
• Often mistaken for no
selection
Example:
Birth Weight
Diversifying (Disruptive) Selection
• Environmental conditions favor individuals at
both extremes of the genetic spectrum and
eliminate or sharply reduce individuals with
intermediate genes.
• It pays to be extreme!!
• Examples:
– Green vs.
Brown Anole
– Darwin’s Finches
Darwin’s Finches
Each finch species is specialized
for a particular lifestyle (structure
of their beaks)
An adaptation to their specific
diets seed eaters, cactus eaters,
insect eaters, fruit eaters) and
different from finches on the
South American mainland.
14 species of Galapagos finches
decended from a single ancestorone or a small population of
finches that originally colonized
the Galapagos.
Types of
Species Evolution
Convergent Evolution
• Two different species who live in the same
type of habitat evolve to have similar traits.
• Example: Sharks and dolphins
– Dolphins are mammals, Sharks are fish.
– So how did they convergently evolve?
• They look the same and act in similar manners
because they both live in the ocean, so they’ll need
similar traits!
CONVERGENT
EVOLUTION
Convergent Evolution
Divergent Evolution
• Two populations of the same species who
live in different places evolve to become
different…
• Example: Birds
– Now we have penguins & puffins!!
– So how do they divergently evolve?
• Penguins live where it’s cold and where there’s lots
of water. There’s more food for them in the water, so
they evolved to “fly” underwater.
• Puffins live where it’s slightly warmer. There’s lots
of food sources outside of the water, so they
continued to fly normally.
Again… Darwin and the birdies
Adaptive
Radiation
process by which
ancestral species
evolve into a
number of diff
species
Divergent Evolution
Divergent Evolution
Coevolution
• Two species that interact closely
may become adapted to one another
He is fast!
I have to
run faster!!
Yummy….
Rabbit for
dinner!
• Example: a wolf and a rabbit
Why
does he
want to
eat me?
I am
sooo
cute!
I will run
faster
then…
– How are they related in an ecosystem?
– So how do they co-evolve?
• If the rabbit evolves to be faster, the wolf will have to
keep up, so it must also evolve to be faster.
Animal/Plant Coevolution
The gracefully
curved bill of the
‘I’iwi enables it to
sip nectar from
flowers of the
lobelia. The ‘I’iwi
bill fits perfectly
into the long tubular
lobelia flowers.
Coevolution in Plants
Acacia Tree & Ant
* Tree has large hollow thorns that provide a
protected nesting site for stinging ants.
Ants attack any animal and clear away
vegetation surrounding the tree which helps
the tree get the sunlight it needs.
Caterpillars & Plants
•Plants may have poisonous
chemicals that prevent insects from eating
them.
•Some caterpillars have the ability to resist
these poisons.
•They can feed on plants that other insects
can’t
•As the plant adapted by producing poisonous
chemicals, the caterpillar adapted by
resisting them.
Coevolution