1. Evolution of Populations and Species
Key Idea: Evolution is change over time. Evolution can occur over of thousands of years, as in the evolution of new species, or it can occur over just a generation or two, as in the evolution of populations.

2. Part 1: Populations
A group of individuals of the same species that live in the same area
In his theory of evolution by natural selection, Darwin stated that not all of the members of a population are able to survive and reproduce. How then do populations grow?

3. Exponential growth:

4. Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate

5. Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate
Will only occur if

6. Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate
Will only occur if there are unlimited resources and conditions are ideal

7. Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate
Will only occur if there are unlimited resources and conditions are ideal

8. Logistic growth:

9. Logistic growth: when a population’s growth slows or stops following a period of exponential growth

10. Logistic growth: when a population’s growth slows or stops following a period of exponential growth
Due to limited resources, most populations in nature experience logistic growth

11. Logistic growth: when a population’s growth slows or stops following a period of exponential growth
Due to limited resources, most populations in nature experience logistic growth

12. Carrying capacity:

13. Carrying capacity: the largest number of individuals that a given environment can support
The carrying capacity can change based on the environment. It is not a fixed number.
If there was a forest fire, the number of trees available to produce nuts would be reduced. As a result the forest could support fewer squirrels.

14. What factors limit population growth and drive the process of evolution?

15. Limiting factor:

16. Limiting factor: a factor that causes population growth to decrease

17. Limiting factor: a factor that causes population growth to decrease
They determine which individuals are able to survive and reproduce

18. Limiting factor: a factor that causes population growth to decrease
They determine which individuals are able to survive and reproduce
Density-Dependent Limiting Factors:

19. Limiting factor: a factor that causes population growth to decrease
They determine which individuals are able to survive and reproduce
Density-Dependent Limiting Factors: a limiting factor that depends on population size

20. Limiting factor: a factor that causes population growth to decrease
They determine which individuals are able to survive and reproduce
Density-Dependent Limiting Factors: a limiting factor that depends on population size
Examples: Competition, predation, parasitism, disease.

21. Limiting factor: a factor that causes population growth to decrease
They determine which individuals are able to survive and reproduce
Density-Dependent Limiting Factors: a limiting factor that depends on population size
Examples: Competition, predation, parasitism, disease.
Density-Independent Limiting Factors:

22. Limiting factor: a factor that causes population growth to decrease
They determine which individuals are able to survive and reproduce
Density-Dependent Limiting Factors: a limiting factor that depends on population size
Examples: Competition, predation, parasitism, disease.
Density-Independent Limiting Factors: factors that affect all populations in similar ways, regardless of population size

23. Limiting factor: a factor that causes population growth to decrease
They determine which individuals are able to survive and reproduce
Density-Dependent Limiting Factors: a limiting factor that depends on population size
Examples: Competition, predation, parasitism, disease.
Density-Independent Limiting Factors: factors that affect all populations in similar ways, regardless of population size
Examples: unusual weather, natural disasters , seasonal cycles

24. How do we know a population is evolving?
Key idea: Populations evolve when the traits of the organisms in the population change over time.

25. Each individual has two copies of a gene, one from each parent
Each individual has two copies of a gene, one from each parent. These copies of genes are called

26. Each individual has two copies of a gene, one from each parent
Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles

27. Each individual has two copies of a gene, one from each parent
Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles
Natural selection on traits can lead to changes in , or how common a version of a gene is in the gene pool of the population

28. Each individual has two copies of a gene, one from each parent
Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles
Natural selection on traits can lead to changes in allele frequency , or how common a version of a gene is in the gene pool of the population

29. Each individual has two copies of a gene, one from each parent
Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles
Natural selection on traits can lead to changes in allele frequency , or how common a version of a gene is in the gene pool of the population
If the allele frequencies of a population are changing, then the population is

30. Each individual has two copies of a gene, one from each parent
Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles
Natural selection on traits can lead to changes in allele frequency , or how common a version of a gene is in the gene pool of the population
If the allele frequencies of a population are changing, then the population is evolving
Last slide 3/14/2011

31. Genetic Equilibrium:

32. Genetic Equilibrium: situation in which allele frequencies remain constant

33. Genetic Equilibrium: situation in which allele frequencies remain constant
If a population is not evolving, the allele frequencies in a population remain stable and genetic equilibrium occurs.

34. Hardy-Weinberg Equilibrium Principle
If these 5 conditions are met, then the population is in equilibrium and is not evolving:
There must be random mating
The population must be very large
There can be no movement into or out of the population
No mutations
No natural selection

35. Is genetic equilibrium common in nature?

36. Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH

37. Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH
Frequency of H
Frequency of h

38. Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH
Frequency of H 16
Frequency of h

39. Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH
Frequency of H 16
Frequency of h 4

40. Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH
Frequency of H 16
Frequency of h 4
Generation 2
Frequency of H
Frequency of h

41. Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH
Frequency of H 16
Frequency of h 4
Generation 2
Frequency of H 13
Frequency of h

42. Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH
Frequency of H 16
Frequency of h 4
Generation 2
Frequency of H 13
Frequency of h 7

43. Did the population evolve from generation 1 to generation 2
Did the population evolve from generation 1 to generation 2? Explain your answer.

44. Part II: Evolution of Species
What is a species?
Biological Species Concept:

45. Part II: Evolution of Species
What is a species?
Biological Species Concept: a group of similar organisms that can breed and produce fertile offspring
Example: Horses and donkeys
When you breed a male donkey and a female horse, you get a mule
Not officially the same species because the mule infertile and so cannot reproduce

46. Problem with BSC: Scientists can’t always observe organisms mating
Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean.
Solution: Scientists can also define species based on , , or .

47. Problem with BSC: Scientists can’t always observe organisms mating
Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean.
Solution: Scientists can also define species based on DNA , , or .

48. Problem with BSC: Scientists can’t always observe organisms mating
Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean.
Solution: Scientists can also define species based on DNA , morphology , or .

49. Problem with BSC: Scientists can’t always observe organisms mating
Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean.
Solution: Scientists can also define species based on DNA , morphology , or niche .

50. Key Idea: New species evolve when populations become reproductively isolated from each other.
Reproductive isolation:

51. Key Idea: New species evolve when populations become reproductively isolated from each other.
Reproductive isolation: separation of a species or populations so that they cannot interbreed and produce fertile offspring

52. Isolating Mechanisms

53. Isolating Mechanisms
Geographic Isolation:

54. Isolating Mechanisms
Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water

55. Isolating Mechanisms
Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water
Behavioral:

56. Isolating Mechanisms
Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water
Behavioral: When two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies

57. Isolating Mechanisms
Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water
Behavioral: When two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies
Temporal:

58. Isolating Mechanisms
Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water
Behavioral: When two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies
Temporal: When two or more species reproduce at different times

59. How did Darwin’s finches become new species
How did Darwin’s finches become new species? They traveled from the mainland to different islands. Once they were on the different islands, they were isolated from each other by the ocean. This is an example of geographic isolation.

60. Key Idea: Only populations and species (which are groups of populations) can evolve. Individuals do NOT evolve.
Creatures don’t “change” from one thing into another…they remain as they were born. Any changes within an organism’s lifetime are due to acquired characteristics. Remember only genetic changes in the egg and sperm will be passed on to offspring.
It is the changes that accumulate over generations in populations or species that lead to changes in organisms over time.

61. Diagramming Evolutionary History
Phylogenetic Tree or Cladograms:

62. Diagramming Evolutionary History
Phylogenetic Tree or Cladograms: diagram that shows the evolutionary relationships among a group of organisms

63. Reading a Phylogenetic Tree or Cladogram:
Species are listed at the end of the branches of the tree.
Time is the vertical axis. If an organism’s branch reaches the present, the species is still around today. If an organism’s branch doesn’t reach the present, it is extinct.
Traits are written on the tree at the time when they evolved. All organisms that branch off after that trait evolved have that trait.

64. Reading a Phylogenetic Tree or Cladogram:
Common ancestors of organisms are represented by the branching points. Organisms that can trace their branches back to that branching point share that common ancestor.
Organisms are more closely related when they share a more recent common ancestor.

66. Practice
Which species is extinct?

67. Practice
Which species is extinct? A

68. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D?

69. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D? C

70. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D? C
Species C is most closely related to which species?

71. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D? C
Species C is most closely related to which species? B

72. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D? C
Species C is most closely related to which species? B
Which species are heterotrophs?

73. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D? C
Species C is most closely related to which species? B
Which species are heterotrophs?
B, C, D

74. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D? C
Species C is most closely related to which species? B
Which species are heterotrophs?
B, C, D
Which species is a carnivore?

75. Practice Which species is extinct? A
What is the most recent common ancestor of Species B and D? C
Species C is most closely related to which species? B
Which species are heterotrophs?
B, C, D
Which species is a carnivore? D

76. Constructing a Phylogenetic Tree or Cladogram:
Organism
Backbone
Legs
Hair
Earthworm
Absent
Trout
Present
Lizard
Human

77. Constructing a Phylogenetic Tree or Cladogram:
Scientists create a character matrix that compares the presence or absence of traits in different organisms.
Based on that information, they can construct a tree.

78. Present
Time
Past

79. Present
Time
Backbone
Past

80. Present
Time
Legs
Backbone
Past

81. Present
Hair
Time
Legs
Backbone
Past

82. Present
Hair
Time
Legs
Backbone
Past

83. Earthworm
Present
Hair
Time
Legs
Backbone
Past

84. Earthworm
Trout
Present
Hair
Time
Legs
Backbone
Past

85. Earthworm
Trout
Lizard
Present
Hair
Time
Legs
Backbone
Past

86. Earthworm
Trout
Lizard
Human
Present
Hair
Time
Legs
Backbone
Past