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Evolution,
Biodiversity, and
Community
Processes
Chapter 5 Notes
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Fossils
• Oldest fossils are the
approximately 3.465
billion-year-old
microfossils from the
Apex Chert, Australia
– colonies of
cyanobacteria
(formerly called bluegreen algae) which
built real reefs
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Fossils
1600's - Danish scientist Nicholas Steno studied
the relative positions of sedimentary rocks
– Layering is the most obvious feature of sedimentary
rocks
• formed particle by particle and bed by bed, and the layers
are piled one on top of the other
• any sequence of layered rocks, a given bed must be older
than any bed on top of it
– Law of Superposition is fundamental to the
interpretation of Earth history, because at any one
location it indicates the relative ages of rock layers
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and the fossils in them.
EVOLUTION
gradual change
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Four causes of evolutionary
change:
1. Mutation: fundamental origin of all genetic
(DNA) change.
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Four causes of evolutionary
change:
1. Mutation: fundamental origin of all genetic
(DNA) change.
Point mutation
…some at base-pair level
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Four causes of evolutionary
change:
1. Mutation: fundamental origin of all
genetic (DNA) change.
Crossing-over
…others at grosser
chromosome level
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Four causes of evolutionary
change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate
different mutations over time.
In a continuous
population, genetic
novelty can spread
locally.
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Four causes of evolutionary
change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations
accumulate different mutations over time.
Local spreading of alleles
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Four causes of evolutionary
change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations
accumulate different mutations over time.
Local spreading of alleles
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Four causes of evolutionary
change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate
different mutations over time.
Spreading process
known as ‘gene
flow’.
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Four causes of evolutionary change
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation  accumulate
mutations
3. Founder Effect: sampling bias during
immigration. When a new population is
formed, its genetic composition depends
largely on the gene frequencies within the
group of first settlers.
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Founder Effect.--
Human example: your tribe had to
live near the Bering land bridge…
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Founder Effect.--
…to invade & settle the ‘New World’!
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Founder Effect
Human examples: consider penal colonies
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Galapagos Finches
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Audeskirk & Audeskirk, 1993
Four causes of evolutionary change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation  accumulation of
mutations
3. Founder Effect: immigrant sampling bias.
4. Natural Selection: differential
reproduction of individuals in the same
population based on genetic differences
among them.
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Four causes of evolutionary
change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation  accumulation of
mutations
3. Founder Effect: immigrant sampling bias.
4. Natural Selection: reproductive race
These 4 interact synergistically
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Evidence of Evolution
1. Biogeography:
Geographical distribution of species
Evidence of Evolution
2. Fossil Record:
Fossils and the order in
which they appear in layers
of sedimentary rock
(strongest evidence)
Evidence of Evolution
5. Comparative
Embryology:
Study of
structures that
appear during
embryonic
development
Old Theories of Evolution
• Jean Baptiste Lamarck (early 1800’s)
proposed:
“The inheritance of acquired
characteristics”
He proposed that by using or not using its
body parts, an individual tends to develop
certain characteristics, which it passes on
to its offspring.
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“The Inheritance of Acquired
Characteristics”
• Example:
A giraffe acquired its long neck
because its ancestor stretched higher
and higher into the trees to reach
leaves, and that the animal’s
increasingly lengthened neck was
passed on to its offspring.
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Charles Darwin
• Influenced by Charles Lyell who
published “Principles of Geology”.
• Darwin realized
–that natural forces gradually change
Earth’s surface
–the forces of the past are still
operating in modern times.
Movement of Earth’s Crust
Sea
level
Sea
level
Sedimentary
rocks form in
horizontal
layers.
When part of
Earth’s crust is
compressed, a
bend in a rock
forms, tilting the
rock layers.
As the surface
erodes due to
water, wind, waves,
or glaciers, the
older rock surface
is exposed.
New sediment is
then deposited
above the
exposed older
rock surface.
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Charles Darwin
• Darwin set sail on the H.M.S. Beagle
(1831-1836) to survey the south seas
(mainly South America and the
Galapagos Islands) to collect plants and
animals.
• On the Galapagos Islands, Darwin
observed species that lived no where else
in the world.
• These observations led Darwin to write
a book
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Giant Tortoises of the Galápagos Islands
Pinta
Pinta Island
Intermediate
shell
Fernandina
Isabela
Tower
Marchena
James
Santa
Cruz
Santa Fe
Hood Island
Floreana
Hood
Saddle-backed
shell
Isabela Island
Dome-shaped shell
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Charles Darwin
Wrote in 1859:
“On the Origin of Species by Means of
Natural Selection”
Two main conclusions:
1. Species were not created in their
present form, but evolved from
ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
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Darwin’s Observations
1. Most species produce more offspring
than can be supported by the
environment
2. Environmental resources are limited
3. Most populations are stable in size
4. Individuals vary greatly in their
characteristics (phenotypes)
5. Variation is heritable (genotypes)
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Natural Selection
• Individuals with favorable traits are
more likely to leave more offspring
better suited for their environment
• Also known as “Differential
Reproduction”
Example:
English peppered
moth (Biston betularia)
Modes of Action
• Natural selection has three modes of action:
1. Stabilizing selection
2. Directional selection
3. Diversifying selection
Number
of
Individuals
Small
Large
Size of individuals
1. Stabilizing Selection
• Acts upon extremes and
favors the intermediate.
Number
of
Individuals
Small
Large
Size of individuals
Stabilizing Selection
• Individuals exhibiting the average
phenotype in a population are selected
for
• Example: Different grass plants in a
population range in length from 8 cm to
28 cm. The 8-10 cm grass blades receive
little sunlight, and the 25-28 cm grass
blades are eaten quickly by grazing
animals.
2. Directional Selection
• Favors variants of one
extreme.
Number
of
Individuals
Small
Large
Size of individuals
Directional Selection
• Individuals at one extreme are favored
• Example: Members of a population of
Amazon tree frogs hop from tree to tree
searching for food in the rain forest. They
vary in leg length. Events result in massive
destruction of the forest’s trees. After
several generations, only long-legged tree
frogs remain alive. (other examples include
the famous peppered moths and bacterial
resistance to antibiotics)
3. Diversifying Selection
•Favors variants of
opposite extremes.
Number
of
Individuals
Small
Large
Size of individuals
Disruptive Selection
• Individuals at both extremes of a range
of phenotypes are favored over those in
the middle – population is split into
two groups – may result in speciation!
• Example: The spines of a sea urchin
population’s members vary in length
The short-spined sea urchins are
camouflaged easily on the seafloor.
However, long-spined sea urchins are
well defended against predators
Modes of Natural Selection
Speciation
• The evolution of new
species.
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Speciation
• When environmental conditions
change, a species must: Evolve
(adapt), Move (migrate), or Die
(extinction)
• # New species - # extinctions =
Biodiversity
• The Extinction of one species
creates an opportunity for another
species to arise
Evidence for
Natural Selection
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Artificial Selection
• The selective breeding of
domesticated plants and animals
by man.
• Question: What’s the ancestor of
the domesticated dog?
Population Genetics
The science of genetic change in
population – Hardy-Weinberg
Population
A localized group of individuals
belonging to the same species
Species
A group of populations whose
individuals have the potential to
interbreed and produce viable
offspring
Gene Pool
The total collection of genes in a
population at any one time
Speciation, Extinction, and Biodiversity
 Speciation
 Geographic isolation
 Reproductive isolation
Fig. 5-8 p. 105
Adaptive
Radiation
Emergence of
numerous species
from a common
ancestor introduced
to new and diverse
environments.
Example:
Hawaiian
Honeycreepers
Convergent Evolution
• Species from different evolutionary
branches may come to resemble one
another if they live in very similar
environments.
• Example:
1. Ostrich (Africa) and Emu (Australia).
2. Sidewinder (Mojave Desert) and
Horned Viper (Middle East Desert)
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Coevolution
• Evolutionary change, in which one
species act as a selective force on a
second species, inducing adaptations
that in turn act as selective force on the
first species.
Example:
1. Acacia ants and Acacia trees
2. Yucca Plants and Yucca moths
3. Lichen
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Extinction
• Background extinction - species disappear
at a low rate as local conditions change
• Mass extinction - catastrophic, widespread events --> abrupt increase in
extinction rate
• Five mass extinctions in past 500 million
years
• Adaptive radiation - new species evolve
during recovery period following mass
extinction
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http://www.geog.ouc.bc.ca/physgeog/contents/9h.html
Mass Extinctions
Date of the
Extinction
Event
Percent
Species
Lost
65 mya
(million
years ago)
85
213 mya
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Dinosaurs, plants (except ferns and
seed bearing plants), marine
vertebrates and invertebrates. Most
mammals, birds, turtles, crocodiles,
lizards, snakes, and amphibians were
unaffected.
Marine vertebrates and invertebrates
248 mya
380 mya
450 mya
75-95
70
50
Marine vertebrates and invertebrates
Marine invertebrates
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Marine invertebrates
Species Affected
Niche
a species’ functional role in its
ecosystem; includes anything affecting
species survival and reproduction
1. Range of tolerance for various physical and
chemical conditions
2. Types of resources used
3. Interactions with living and nonliving
components of ecosystems
4. Role played in flow of energy and matter cycling
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Niche is
the species’ occupation
and its
Habitat
location of species
(its address)
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Niche
Fundamental niche: set
of conditions under which
a species might exist in the
absence of interactions
with other species
Realized niche: more
restricted set of conditions
under which the species
actually exists due to
interactions with other species
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