16-3 The Process of
Speciation
I. Isolating Mechanisms
1. Species- A
group of
organisms that
breed with one
another and
produce fertile
offspring
2. Speciation- the
formation of a
new species
Horse
+
Donkey
= Mule which is sterile and therefore not
a species
Discuss w/ Partner:
O What factors are involved in the formation of
new species?
Answer:
O What factors are involved in the formation of
new species? The gene pools of two
populations must become separated for
them to become new species.
As new species evolve,
populations become
reproductively
separated from each
other.
4. Reproductive IsolationWhen the members of
two populations can’t
interbreed & produce
fertile offspring
5. Reproductive Isolation
results in separate gene
pools.
3.
6. The 3 causes of
reproductive
isolation:
a) Behavioral
Isolation
b) Geographic
Isolation
c) Temporal
Isolation
7.
Behavioral
Isolation- when two
populations are
able to interbreed
but different
courtship rituals or
other reproductive
strategies that
involve behavior.
Different species of bowerbird construct
elaborate bowers & decorate them with
different colors in order to woo females.
The Satin bowerbird (left) builds a channel
b/w upright sticks, and decorates with
bright blue objects, while the MacGregor’s
Bowerbird (right) builds a tall tower of
sticks and decorates with bits of charcoal.
Evolutionary changes in mating rituals,
such as bower construction, can
contribute to speciation.
8. Geographic
Isolation - when
two populations
are separated by
geographic
barriers such as
rivers or
mountains.
9.
Temporal Isolationwhen two or more
species reproduce
at different times
Discuss w/ Partner:
O Pg. 406 Figure 16-13
O The woodpecker finch uses its beak to hold
a cactus spine, which pokes into holes in
tress in order to spear insects.
1. What tool does its beak resemble?
2. If another species of fruit-eating finch was
discovered, what type of beak do you think
it would have?
Answers:
What tool does its beak resemble? Pliers
or needle-nosed pliers.
2. If another species of fruit-eating finch was
discovered, what type of beak do you think
it would have? It would have a beak like
the vegetation tree finch which also eats
fruit.
1.
Discuss w/ Partner:
O Figure 16-15 page. 407
1.
How would the graph be different if birds
with medium-sized beaks were more likely
to survive?
Answer:
1.
How would the graph be different if birds
with medium-sized beaks were more likely
to survive? It would resemble a normal
curve (bell shaped curve)
II. Speciation in Darwin’s
Finches
1.
Speciation in the Galápagos finches
occurred by:
a)
b)
c)
d)
e)
founding of a new population
geographic isolation
changes in new population's gene pool
reproductive isolation
ecological competition
Founders Arrive- A
few finches—
species A—travel
from South
America to one of
the Galápagos
Islands.
3. There, they survive
and reproduce
2.
Geographic
Isolation- Some
birds from species
A cross to a second
island.
5. The two
populations no
longer share a
gene pool.
4.
6.
7.
Changes in the Gene
Pool- Seed sizes on
the second island
favor birds with large
beaks.
The population on
the second island
evolves into
population B, with
larger beaks.
8.
9.
Reproductive
Isolation- If
population B birds
cross back to the
first island, they will
not mate with birds
from population A.
Populations A and B
are separate
species.
10. Continued Evolution-
This process of
isolation, genetic
change, and
reproductive
isolation probably
repeated itself often
across the entire
Galápagos island
chain.