Title: Chapter 16 Natural selection on traits Speciation
1Chapter 16Natural selection on traits Speciation
2Natural 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.
3In this case, birds with larger beaks have higher
fitness. Therefore, the average beak size
increases.
4Human babies born at an average mass are more
likely to survive than babies born either much
smaller or much larger than average.
5If average-sized seeds become scarce, a bird
population will split into two groups one that
eats small seeds and one that eats large seeds.
6Speciation
- - 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
7How it begins
- The gene pools become separated
- Artificially or naturally
- Species reproduce and adapt to new habitats
8Isolation 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.
9Reproductive isolation
- 3 Types
- Behavioral isolation
- Temporal isolation
- Geographic isolation
10Behavioral Isolation
- Two populations have differences in courtship
rituals and courtship behaviors that prevent them
from interbreeding.
11Temporal Isolation
- Occurs when two or more species reproduce at
different times.
12Geographic Isolation
- Populations are separated physically by
geographic barriers. - Ex. Rivers, mountains, or other large bodies of
land/water
13Testing 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.
15Speciation 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!
16Question 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.
17Question 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.
18Question 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.
19Question 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.
20Question 5
- Beak size in the various groups of Galápagos
finches changed primarily in response to - climate.
- mating preference.
- food source.
- availability of water.