1. Evolution by Means of Natural Selection: Mechanisms of Natural Selection

2. Important Vocabulary
Adaptation: physical or behavioral trait that helps an individual survive & reproduce in its environment.
Makes them more “fit”
Fit or Fitness: success at surviving & reproducing; “Survival of the Fittest”
Natural Selection: adaptations being selected for increase an individual’s fitness in the environment
Artificial Selection: Nature provided the variation, and humans selected those variations that they found useful.
How does its coloration help the Snowy Owl survive in its habitat?
What other adaptations does it have that makes it “fit” for its environment?

3. Natural Selection at Work: The Peppered Moths
Before
After
Before the industrial revolution in England (1850), the frequency was higher for light peppered moths than the dark peppered moths.
After the start of the industrial revolution, the frequency of dark peppered moth was higher than the light peppered moth.

4. Requirements for Natural Selection: 1. Variation Exists in Nature
Variation is inheritable.
Some variations are harmful, some are helpful and some are neutral.
Biodiversity – Biological diversity; Sum total of the genetically based variety of all organisms in the biosphere.

5. Requirements for Natural Selection: 2
Requirements for Natural Selection: 2. More offspring are produced than will survive.
Tendency towards overpopulation
Strategy for survival: Many species lay many eggs in hopes that some will survive to adulthood in order to reproduce.

6. Predator / prey relationships create strong pressure for change
Requirements for Natural Selection: 3. There is a constant struggle for survival.
Competition for limited food supply, space, territory, shelter (nesting sites) & mates
Predator / prey relationships create strong pressure for change
Wolf chasing raccoon

7. Requirements for Natural Selection: 4
Requirements for Natural Selection: 4. Some individuals in the species will have variations that cause them to be the most fit in a particular environment.
The fittest individuals will survive the longest & produce more offspring than less “fit” individuals.
The most “fit” individuals are best adapted to that particular environment.
If environment changes, different variations may be selected to be more fit

8. Requirements for Natural Selection: 5
Requirements for Natural Selection: 5. Vast amount of time is required for a species to change
After many generations there will be enough genetic change in the population to produce a new species.
Separated by a glacier during the last Ice Age, two different species of meadowlark evolved.
Eastern Meadowlark
Western Meadowlark

9. Mutations in Genes: the Source of all new Variations
Helpful mutations lead to adaptation by increasing fitness & decreasing the death rate
Frequency of helpful mutation (gene) will increase in the population as more individuals survive & leave offspring
Harmful mutations will decrease fitness of the individual in that environment & cause a higher mortality rate
Frequency of the mutation (gene) will decrease & might or might not disappear from the gene pool
Gene Pool - Consists of all genes, including all the different alleles, that are present in a population.
How is the fruit fly on the bottom different from the fruits above?

10. Adaptations of Birds Feet
Helpful Adaptations
The woodpecker’s sharp beak allows it to drill into trees to catch insects.
Adaptations of Birds Feet

11. Helpful Adaptations
The giraffe’s long neck helps it reach higher in the tree for food where other animals can’t.
The alternating black & white stripes help keep zebras cool. Black stripes absorb heat & white stripes reflect heat.

12. Adaptations: A Result of Compromise
An adaptation may work really great for some things (reaching food) , but they may prose a problem for other things (drinking water).

13. Adaptations That Increase Fitness are Inherited Variations!
Remember: Individuals Cannot Change to Fit the Environment!
Adaptations That Increase Fitness are Inherited Variations!

14. Camouflage: A Helpful Adaptation
Camouflage: having a shape or color that blends in with the environment
Difficult for predators to see the prey
Find the canyon tree frog!
Find the green leaf mantis!

15. Mimicry: Taking Advantage of Another’s Coloration
Mimicry: when a harmless individual looks like a similar, harmful (poisonous) individual
Predators learn to avoid both
Viceroy: looks like poisonous monarch
Monarch is poisonous

16. Other sources of variation
Natural selection is not the only source of evolutionary change. In small populations, an allele can become more or less common simply by chance.
1. Genetic Drift - Random change in allele frequencies that occurs in small populations.
It happens by chance - such as random mating or a natural disaster (fire, landslide or lightning strike).
Doesn’t work to produce adaptations like natural selection does.

17. 2. Gene Flow - The transfer of alleles or genes from one population to another; also known as gene migration.
Affected by:
Mobility
Barriers

18. What mechanisms lead to speciation?
SPECIES - A GROUP OF SIMILAR LOOKING ORGANISMS THAT CAN BREED TOGETHER TO PRODUCE FERTILE OFFSPRING. (FERTILE-ABLE TO REPRODUCE).

19. Reproductive Isolation Leads to Speciation
Speciation: Members of an original species can no longer breed together to produce fertile offspring. They are considered 2 separate species.
Three species of Flycatcher. Reproductive Isolation keeps these as three separate species. Why?
Females only respond to mating call (song) of males that are like them. This is an example of behavioral isolation.

20. What mechanisms lead to reproductive isolation?
Grand Canyon is NOT a physical barrier for all species. What kind of organisms would be able to cross the canyon?
Geographic isolation: a barrier that physically separates members of a species into two or more groups
EX: Mountains, large body of water (lake or ocean), volcanic eruption, canyon, road
A barrier may physically separate some species, but not others

21. Reproductive isolation can occur by:
2. Behavioral Isolation: Two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior
blue footed booby video:
A blue-footed booby displaying his brightly colored feet

22. 3. Temporal Isolation - Form of reproductive isolation in which two populations reproduce at different times.
Example:
Three similar species of orchid all live in the same rain forest.
Each species releases pollen only on a single day.
Because the three species release pollen on different days, they cannot pollinate one another.

23. Food becomes scarce. Notice the shift in beak size
Three types of Natural Selection in Populations: A. Directional Selection
Directional selection: members at one end of distribution curve have a higher fitness than those in the middle or at the other end of the curve.
Can lead one population evolving into a new species.
Food becomes scarce. Notice the shift in beak size

24. Directional Selection
Selection for longer beaks
The woodpeckers with the longer beaks are more fit for this environment, so there are more of them than woodpeckers with shorter beaks.

25. B. Stabilizing Selection
Stabilizing selection: members in the center of the distribution curve have a higher fitness than those at each end.
This type of selection favors average individuals.
Reduces variation in a population; evolution is not likely to happen.
Ex: babies that are between 6 & 8 pounds at birth have a better chance of surviving 1st year of life.

26. Stabilizing Selection
In the example below, averaged size spiders survive more often, because birds eat the very large and small ones.

27. C. Disruptive Selection
Disruptive selection: when members at BOTH ends of the distribution curve have a higher fitness than those in the middle
In some cases, there are no intermediate forms.
This can lead to the evolution of two new species.
Population splits into two subgroups specializing in different seeds.
Number of Birds in Population
Beak Size

28. Selection for dark limpets
Disruptive Selection
In the example below, the light and dark limpets (Clams) are camouflaged, whereas the intermediate ones are not, and are eaten.
Selection for dark limpets

29. Matching Practice (Types of Selection):
Does not lead to speciation or evolution.
Cause one species to evolve into two different species.
Causes one species to evolve into a different species.
Type of selection that favors one extreme variation.
Type of selection that favors the average variation.
Type of selection that favors the two extreme variations.
A. Directional
B. Stabilizing
C. Disruptive

30. Gradualism, Punctuated Equilibrium and Genetic Equilibrium
How long does it take for evolution to occur?
Does evolution always occur?

31. Gradualism vs. Punctuated Equilibrium
How quickly does evolution occur?
Gradualism – Long time with gradual change.
Punctuated Equilibrium - Long, stable periods interrupted by brief periods of more rapid change.

32. Evolution vs. Genetic Equilibrium
To clarify how evolutionary change operates, scientists often find it helpful to determine what happens when no change takes place.
So biologists ask: Are there any conditions under which evolution will not occur?
The answers to those questions are provided by the Hardy-Weinberg principle.

33. Hardy-Weinberg Principle
Five conditions are required to maintain genetic equilibrium from generation to generation:
There must be random mating.
The population must be very large.
Genetic drift has less effect on large populations than on small ones.
There can be no movement into or out of the population.
Individuals may bring new alleles into a population.
There can be no mutations.
There can be no natural selection.
No phenotype can have a selective advantage over another.

34. Two Patterns of Evolution-
1. Adaptive Radiation or Divergent Evolution type of evolution in which one species evolves into two separate species because it is adapting to different environmental situations
2. Convergent Evolution- type of evolution in which two unrelated species evolve similar characteristics because they are both adapting to the same environmental situations

35. Divergent Evolution or Adaptive Radiation
Raven and Johnston, Biology
Divergent Evolution
or Adaptive Radiation

36. Raven and Johnston, Biology
Divergent Evolution

37. Raven and Johnston, Biology
Convergent Evolution