Download File - BIOLOGY and HONORS PHYSIOLOGY Mr. Wylam

Patterns of
Evolution
Patterns of Evolution: Sections
1. Adaptive Radiation
2. Mechanisms of Speciation
3. Convergent vs. Divergent
4.
5.
6.
7.
8.
Evolution
Co-evolution
Models of change:
Gradualism vs. Punctuated
Equilibrium
The Evolution of Populations
Modes of Selection
Intra vs. Intersexual
Selection
Adaptive Radiation: General
• adaptive radiation
occurs when an ancestral
species develops into
many different species
filling different
environmental niches.
• General adaptation is
advantageous for
accessing previously
unreachable resources
(natural selection).
modifies
homologous
structures
Adaptive Radiation Modifies homologous structures
Adaptive Radiation: Environmental
• Environmental
adaptation occurs
when species adapt
in response to an
environmental
change.
• Examples: Extended
period of drought or
flooding, geographic
isolation
Adaptive Radiation: Archipelagoes
• Archipelagoes involve
the colonization of
secluded environments,
usually islands, and
through isolation, permit
rapid variation in species
due to a decrease in
outside environmental
factors.
Mechanisms of Speciation
Temporal Isolation
• Temporal Isolation
occurs because species
mate at different times
• Examples: Plants
flower at different
times throughout the
year, various species of
fireflies mate at
different times of the
night.
Mechanisms of Speciation:
Geographic Isolation
• Geographic Isolation
occurs when a segment of a
population (of the same
species) become separated by
a physical barrier (body of
water, mountains, etc.) and
speciation occurs over time.
Mechanisms of Speciation
Behavioral Isolation
• Behavioral isolation
mechanisms involve
variance in courtship
behavior, differences in
vocalization, and/or
phememones which
effectively create and
maintain boundaries
within closely related
species.
Divergent Evolution
• Divergent evolution is the
accumulation of differences
between groups (due to
different environmental
pressures) which eventually
leads to speciation (the
forming of a new species)
• **Different examples, types,
and modes of divergent
evolution will be visited
throughout this presentation…
Convergent Evolution
• Convergent evolution
describes the acquisition
of similar traits in
unrelated lineages* due
to comparable
environmental niches in
different parts of the
world.
• Examples: marsupials,
*All species share a common ancestry
wing development
Convergent Evolution
These animals have evolved similar adaptations
for obtaining food because they occupy similar
niches.
Co-evolution
•When 2 interdependent species influence each
others morphology, it is referred to as
co-evolution
Models of Macroevolution:
Gradualism
• Evolutionary change is both
slow and gradual
• Resulting from the
accumulation of many small
genetic changes favoured by
natural selection
• Other effects occasionally
making small contributions
Models of Macroevolution:
Punctuated Equilibrium
“instead of a slow,
continuous movement,
evolution tends to be
characterized by long periods
of virtual standstill
("equilibrium"), "punctuated"
by episodes of very fast
development of new forms”
-Stephen Jay Gould
Stasis and change:
The P.E. Model
• A species resists evolutionary change
• A species would rather move to a new area
where it can find its habitat than adapt to a new
one
• If a small population of a species should get
isolated in an area where its habitat does not
exist…
• …rapid change could take place to bring the
population back to equilibrium (stasis)
• But it is no longer the same species
Species Y
Species Z
Species X
Stasis
Species W
Stasis
Time
Rapid
speciation
Stasis
Rapid
speciation
Evolution
Rapid
speciation
The Evolution of Populations:
Genetic Drift
• The “gene pool” refers to
the unique set of alleles
(within a species) for any
given trait in a given
population.
• Genetic Drift is the natural
shifting of allele frequency
within a population over
time. In the absence of
outside interference, genetic
drift is minimal…
Gene Flow:
The Bottleneck Effect
• When population size is drastically reduced,
abnormal allele frequencies may exist in the
survivors, resulting in a loss in genetic variation.
Gene Flow:
The Founder Effect
• the founder effect reflects a decrease in
genetic variation occurring when a new
population is established by a very small
number of individuals “transplanted” from a
larger population.
Factors Influencing
The Evolution of
Populations
Modes of Natural Selection:
Directional Selection
• For a given population, selection against
one extreme can favor a specific
phenotype and result in directional
selection.
Directional Selection: An Example
• The first breeders of hound
dogs were focused exclusively
on speed, they favored and
bred the fastest dogs. By
continuing this selection for
those dogs who ran faster
than most of the hound dog
population, they gradually
produced a dog who could run
up to 40 mph!
Modes of Natural Selection:
Stabilizing Selection
• Stabilizing Selection takes place when
selection favors the intermediate
phenotype over the extreme values.
Stabilizing Selection: An Example
• A good classic example of this is lion birth
weight. Cubs of low weight lose heat more
quickly and get ill from infectious disease more
easily, whereas cubs of large body weight are
more difficult to deliver through the pelvis.
Modes of Natural Selection:
Disruptive Selection
• Disruptive selection favors both
extreme phenotypes, while those with the
intermediate are selected against.
Disruptive Selection: An Example
Intrasexual Selection
• Intrasexual Selection is
associated with
characteristics affecting the
outcome of competition the
male members of one
species for access to the
female.
• Almost always, males among
the most genetically “fit”
pass their genes on,
ensuring the overall fitness
of the population and the
species as a whole.
Intersexual Selection
• Intersexual selection
involves the females
“Choosing” their mates
based on characteristics
which ‘stand out.’
• Unique colors, physiologic
features, and elaborate
courtship behaviors have
evolved among nearly all
species in response to
intersexual selection
I have called this principle, by which
each slight variation, if useful, is preserved,
by the term Natural Selection.
—Charles Darwin from "The Origin of
Species"
That’s All
Folks!