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Chapter 16 Natural selection on traits Speciation

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Title: Chapter 16 Natural selection on traits Speciation


1
Chapter 16Natural selection on traits Speciation
2
Natural selection on physical traits
  • Natural selection can affect the distribution of
    genes that control physical traits in any of
    three ways
  • Directional when individuals at one end of the
    curve have higher fitness than individuals in the
    middle or at the other end
  • Stabilizing- when individuals near the center of
    the curve have higher fitness than individuals at
    either end of the curve
  • Disruptive individuals at the upper and lower
    ends of the curve have higher fitness than
    individuals near the middle.

3
In this case, birds with larger beaks have higher
fitness. Therefore, the average beak size
increases.
4
Human babies born at an average mass are more
likely to survive than babies born either much
smaller or much larger than average.
5
If average-sized seeds become scarce, a bird
population will split into two groups one that
eats small seeds and one that eats large seeds.
6
Speciation
  • - Definition
  • A species is a group organisms that are able to
    breed with one another and produce fertile
    offspring.
  • Speciation is the formation of new species

7
How it begins
  • The gene pools become separated
  • Artificially or naturally
  • Species reproduce and adapt to new habitats

8
Isolation Mechanisms
  • As new species evolve, populations become
    reproductively isolated from each other.
  • As species evolve their DNA changes and
    eventually the 2 populations cannot interbreed
    and produce fertile offspring, this is known as
    reproductive isolation.

9
Reproductive isolation
  • 3 Types
  • Behavioral isolation
  • Temporal isolation
  • Geographic isolation

10
Behavioral Isolation
  • Two populations have differences in courtship
    rituals and courtship behaviors that prevent them
    from interbreeding.

11
Temporal Isolation
  • Occurs when two or more species reproduce at
    different times.

12
Geographic Isolation
  • Populations are separated physically by
    geographic barriers.
  • Ex. Rivers, mountains, or other large bodies of
    land/water

13
Testing Natural Selection/Speciation in Nature
  • Using Darwins Finches
  • He concluded they were different species but they
    had descended from a common ancestor.
  • He looked at
  • Food / Diet
  • Body / Beaks
  • Habitat

14
  • For beak size and shape to evolve, there must be
    enough heritable variation in those traits to
    provide raw material for natural selection.
  • Differences in beak size and shape must produce
    differences in fitness, causing natural selection
    to occur.

15
Speciation in Darwin's Finches
  • Ecological Competition
  • As species A and B compete for available seeds on
    the first island, they continue to evolve in a
    way that increases the differences between them.

A new species C may evolve!
16
Question 1
  • When two species do not reproduce because of
    differences in mating rituals, the situation is
    referred to as
  • temporal isolation.
  • geographic isolation.
  • behavioral isolation.
  • reproductive isolation.

17
Question 2
  • The most important factor involved in the
    evolution of the Kaibab and Abert squirrels of
    the American Southwest appears to be
  • temporal isolation.
  • geographic isolation.
  • behavioral isolation.
  • different food sources.

18
Question 3
  • One finding of the Grants' research on
    generations of Galápagos finches was that
  • natural selection did not occur in the finches
  • natural selection can take place often and very
    rapidly.
  • beak size had no effect on survival rate of the
    finches.
  • natural selection was slow and permanent.

19
Question 4
  • All of the following played a role in speciation
    of Galápagos finches EXCEPT
  • no changes in the gene pool.
  • separation of populations.
  • reproductive isolation.
  • natural selection.

20
Question 5
  • Beak size in the various groups of Galápagos
    finches changed primarily in response to
  • climate.
  • mating preference.
  • food source.
  • availability of water.
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