Download Process of Speciation - James Monroe High School

Process of Speciation
Ch 16.3
Intro to Speciation
Recall, biologists define a species
as a group of individuals that breed
and produce fertile offspring
Intro to Speciation
Therefore individuals of the same
species share a common gene pool.
Intro to Speciation
As genetic change
occurs in one individual,
it can spread through
the population via
its offspring.
Intro to Speciation
If this change increases “fitness” it will
soon be found in many within the
population.
Speciation
 Defined
asThe formation of
new species
 As new species evolve,
populations become
reproductively isolated
Reproductive Isolation
 Defined
asWhen members of two
populations cannot interbreed
* Breeding can be prevented due
to changes in behavior (eating,
mating rituals, timing)
environment (niches, food
source, geographic barriers) or
mechanics (breeding,
fertilization, development)
Isolating Mechanisms
Reproductive isolation can occur
as a result of:
Behavioral Isolation
Geographic Isolation
Temporal Isolation
Mechanical Isolation
Behavioral Isolation
Defined as- the isolating mechanism that
operates through differences in
courtship behavioral patterns
 Different mating location, mating time, or
mating rituals
 If one species
displays a
certain courtship
pattern,
it won’t be
recognized by
those of the
other species

Behavioral Isolation
 This
is the mechanism which
separates wolfs from dogs,
their courtship
patterns are different
in the wild
Behavioral Isolation
Meadowlarks
Western
Eastern
Behavioral Isolation
 Difference
in
courtship rituals
Western and
Eastern Meadowlark
(Different mating
songs)
Behavioral Isolation
Different species of bowerbird construct elaborate
bowers and decorate them with different colors in
order to woo females. The Satin bowerbird (left)
builds a channel between 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.
Behavioral Isolation
 Feeding
Habits
- change in food
preference
No gene flow occurs now
because they eat, mate,
and lay their eggs on
different hosts (fruit).
Fruit flies switched from
Hawthorn fruit to Apple fruit
introduced from England
Geographic Isolation
 When
two populations are separated
physically when their original habitat
becomes divided by barriers such as
rivers,
mountains,
or bodies
of water
Geographic Isolation
 Another
Example of Speciation due
to Geographic Isolation
(Colorado River – 10,000 years ago)
Abert Squirrel
Kaibab Squirrel
(Sciurus aberti)
(Sciurus aberti
kaibabensis)
Grand Canyon
Geographic Isolation
Island/Bodies
of water

Separated the
Galapagos finches,
tortoises, iguanas,
and other species
Geographic Isolation




Speciation in action?
In the summer of 1995, at least 15 iguanas
survived Hurricane Marilyn on a raft of uprooted
trees.
They rode the high seas for a month before
colonizing the Caribbean island, Anguilla.
Evolutionary biologists would love to know what
happens next:
– will the colonizing iguanas die out,
– will they survive and change only
slightly, or
– will they become reproductively
isolated from other Iguana iguana
and become a new species?
Temporal Isolation
 Two
or more species reproduce
at different times.
 The time periods could differ
simply by hours,
or by seasons
Temporal Isolation
 If
one species reproduces in the
spring, while the other
reproduces in the fall, the two
species aren’t able to breed
Temporal Isolation
Example:
3 similar species of
orchid in same forest
release pollen on
different days
(can not pollinate
one another)
Mechanical Isolation
 Deals
with the actual mechanics of
the reproductive organs
 Occurs when there is incompatibility
in structure of the male and female
sex organs
Mechanical Isolation
 Isolates
species by preventing
mating between two different species
 Isolation also occurs when the
gametes of the two species are
chemically incompatible
 Prevents fertilization
Darwin’s Discovery
Galapagos
Island Finches
Darwin’s Discovery
The finches looked so
different he thought
they were blackbirds,
warblers, & other kinds
of birds.
After returning home,
an ornithologist told
him they were all
finches
Darwin’s Discovery
He then hypothesized:
– They had descended from a common
ancestor.
– Natural selection shaped the beaks as
they adapted to eat different foods
Concept Map
Reproductive Isolation
results from
Isolating mechanisms
which include
Behavioral isolation
Geographic isolation
Temporal isolation
produced by
produced by
produced by
Behavioral differences
Physical separation
Different mating times
which result in
Independently
evolving populations
which result in
Formation of
new species
Speciation of Finches in the
Galapagos Islands
A
A
A
Galapagos
Islands
South
America
a) Founders Arrive
A
B
b) Separation of Populations
c) Changes in the Gene Pool
E
A
B
A
B
d) Reproductive Isolation
B
C
e) Ecological Competition
A
D
B
C
f) Continued Evolution