Transcript Ch16.3 Process of Speciation

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 in the same
species share a common gene pool.
As genetic change occurs in one
individual, it can spread through the
population via its offspring.
If this change increases “fitness” it will
soon be found in many within the
population.
Isolating Mechanisms
As new species evolve, populations
become reproductively isolated.
Reproductive isolation can occur as a
result of:
Behavior Isolation
Geographic Isolation
Temporal Isolation
Behavioral Isolation
 Difference
in
courtship rituals
Western and Eastern Meadowlark
(Different mating songs)
Behavioral Isolation
 Feeding
Habits
- change in food
preference
No gene flow occurs now because
they eat, mate, and lay their
eggs on different hosts now.
Fruit flies switched from Hawthorn
fruit to Apple fruit introduced from
England
Rhagoletis pomonella
Geographic Isolation
 Two
Populations are separated 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
(Sciurus aberti)
Kaibab Squirrel
(Sciurus aberti kaibabensis)
Temporal Isolation
 Two
or more species reproduce at
different times.
Example:
3 similar species of
orchid in same forest
release pollen on
different days (can not
pollen one another)
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
Testing Natural Selection in Nature
Peter and Rosemary Grant of
Princeton University decided to test
Darwin’s hypothesis. They figured it
relied on two testable assumptions.
1. Sufficient Variation among
species
2. Natural Selection due to
“fitness” of the variation
Testing Natural Selection in Nature
What the Grant’s Finch
Research Showed:

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
There is great variation
among inheritable traits
During drought, food
becomes scarce or gone
and big beaks more likely
to survive.
Big beak birds tend to mate
with other big beak birds,
resulting in increase in average
beak size of the population
The next generation of finches
had bigger beaks than the generations
before
Testing Natural Selection in Nature
After 20 years of banding
& measuring finches, the
Grants had demonstrated
that evolutionary changes
in finch beak size & shape
occur rapidly in response
to severe environmental
changes in the Galapagos
Peter and Rosemary Grant
(Princeton University)
Follow these Steps as Review of
Speciation in Darwin’s Finches
1. Founders Arrive
on an Island
2. Separation of
Population
(some birds of
species A cross to
another island)
3. Change in Gene Pool
(natural selection
causes species A & B
to evolve.)
4. Reproductive
Isolation (now even
if species A & B
appear in same
locale, gene pool
remains isolated)
5. Ecological
Competition
(increase difference
as species A & B
compete.)
6. Continued Evolution