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CHAPTER
5
Evolution and Community
Ecology
Black and White, and Spread
All Over
• Zebra mussels and quagga mussels were accidentally
introduced into Lake St. Clair in the late 1980s.
• They have since spread throughout the Great Lakes
system and connecting rivers.
• The invasive mussels have a high economic and
ecological cost.
Talk About It The Great Lakes are home to more than
20 native mussel species. Why are the zebra and
quagga mussels so much more destructive than the
lakes’ native mussels?
Lesson 5.1 Evolution
Scientists have identified
and described
over 1.5 million species.
Millions more
have yet to be discovered.
Lesson 5.1 Evolution
Evolution and Natural Selection
• Gene: A sequence of
DNA that codes for a
particular trait
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A starting population of fish. Genes control
the color and pattern of the fish’s scales.
• Gene pool: All the genes
present in a population
• Biological evolution:
The change in a
population’s gene pool
over time
Lesson 5.1 Evolution
Mechanisms of Biological
Evolution: Mutation and Migration
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Mutation
Accidental change in DNA
that can give rise to
variation among individuals
Migration (gene flow)
Movement of individuals into
(immigration) or out of (emigration)
a population
Lesson 5.1 Evolution
Mechanisms of Biological
Evolution: Genetic Drift and
Natural Selection
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Genetic Drift
Evolution that occurs by chance
Natural Selection
Process by which traits useful for
survival and reproduction are passed on
more frequently than those that are not
Lesson 5.1 Evolution
Conditions of Natural Selection
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(1) Organisms
produce more
offspring than can
survive.
(2) Individuals vary in
characteristics, some
of which are heritable.
(3) Individuals vary in
fitness, or reproductive
success.
Did You Know? Darwin privately
researched natural selection for two
decades before publishing On the Origin of
Species.
Lesson 5.1 Evolution
Artificial Selection
• Selection under human direction
• Throughout history, humans have chosen and bred
animals and plants with beneficial traits.
Lesson 5.1 Evolution
Speciation
•
Process by which
new species are
generated
•
Can occur in a
number of different
ways; the most
important way is
called allopatric
speciation
•
Has resulted in every
form of life on Earth—
today and in the past
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Allopatric Speciation
Lesson 5.1 Evolution
Extinction
• The disappearance of
species from Earth
Trilobites
Marine arthropods that went extinct at
the end of the Permian period.
Did You Know? During the Permo-Triassic
extinction 250 million years ago, 70% of all
land species and 90% of all marine species
went extinct.
• Generally occurs gradually,
one species at a time,
when environmental
conditions change more
rapidly than the species
can adapt
• There are five known mass
extinction events, each of
which wiped out a large
proportion of Earth’s
species.