Transcript evolution - Cloudfront.net

Overview
Evolution Section
16-2
Genetic Drift
 Genetic Drift– can cause allele
frequencies to change based on chance
 Based on these two examples
 Founder effect
 Bottleneck effect
Types of Natural Selection
 Directional selection
 Example
of Darwin’s Beak Size
 Disruptive selection
 Acts
against the intermediate type and
favors two Distinct subpopulations
 Stabilizing selection
 Keeps
phenotypes stable for long periods
of time. Example (Babies birth’s weights
 Are 6 to 8 pounds
Chapter 16-3
and Ch 17-4
Evolution Mechanisms
The Process of Speciation
Speciation: Formation of New
Species
Reproductive isolation must be
achieved!
Reproductive Isolation
 4a This occurs when the members of
two populations cannot interbreed
and thus become reproductively
isolated -causing separation of Gene
Pools
 4b. And Ultimately new species arrive.
Behavioral Isolation
 Occurs when two populations are
capable of inter-breeding but choose
not-to because of different courtship
rituals or other reproductive strategies.
Isolation in Cheetahs
Behavioral isolation is important because it
prevents one species from breeding with
another species. Observations of complete
courting behavior and mating of cheetahs in
the wild are very rare.
 First, their basic courting behavior is
similar to other cats.
 Second, we know that breeding
behavior within a species is often highly
ritualized and there are distinct
differences between closely related
species.
Cheetah Example
 If a particular breeding sequence is
altered in anyway,
 breeding does not occur.
 We can only assume that there are
enough differences in breeding behavior
of the cheetah so that it cannot breed
with the lions and leopards that are
found in the same
Geographic Isolation
 This occurs when two populations are
seperated by geographic barriers such
as a river or a canyon or large bodies of
water.
Temporal Isolation
Example: When two or more species
reproduce at two different times or
seasons.
Types of Speciation
 Allopatric Speciation
 Geographic
 Adaptive
isolation –
Radiation- A process by which a
single species or a group of species
evolve into several different forms that live
in different ways. (Fossil Record as
Evidence)
Convergent Evolution
 A process of evolution when unrelated
organisms come to resemble one
another.
 Evidence:
Homologous Structures- Flippers of
Dolphins have similar Wings of
Penguins.
Convergent Evolution
 Sympatric Speciation
 Almost
always in plants
 In same population but do not interbreed
 Coevolution: The Process by which two
species evolve in response to changes
in each other over time.
Rates of Evolution
Gradualism vs.
Punctuated Equilibrium
Punctuated Equillibrium
 a theory in evolutionary biology. It states
that most sexually reproducing
populations will show little change for
most of their geological history, and that
when phenotypic evolution does occur.
Gradualism Theory
 phyletic gradualism, which states that
evolution generally occurs uniformly and
by the steady and gradual
transformation
 In this view, evolution is seen as
generally smooth and continuous.
The Two Competing Theories
#16
 Giraffes and zebras both came from a
common ancestor,
 But the theorists describe it as different
patterns in evolution
Questions for Video to answer
 #1What do the Rough Skinned Newts
do to protect themselves from the
predators?
 #2. What has happened to the poison
levels’ in the toxic newt’s response to
the snake?