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Evolution Unit. Evolution of Populations. What is a population?. Number of Individuals of the Same Species that Live together in one area or place. Population. Factors That Control Population Growth. A population’s biotic potential is the size it would be if nothing stopped it.

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Evolution of Populations

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Evolution unit

Evolution Unit

Evolution of Populations


Population

What is a population?

Number of Individuals of the

Same Species that

Live together in one area or place

Population


Factors that control population growth

Factors That Control Population Growth

  • A population’s biotic potential is the size it would be if nothing stopped it.

  • Why don’t populations grow indefinitely?


Factors that control population growth1

What determines the population number of an ecosystem (or planet)?

(Think in terms the basics that plants, animals and ourselves need to survive.)

Factors That ControlPopulation Growth


Factors that control population growth2

Populations don’t grow indefinitely because of Limiting Factors.

The major limiting factors are FWSS:

Food

Water

Shelter

Space

Factors That Control Population Growth


Factors that control population growth3

Carrying Capacity is the maximum number of individuals the environment can support.

Carrying capacity is closely associated with the availability of limiting factors.

Factors That Control Population Growth


Factors that control population growth4

?

?

carrying capacity

Factors That Control Population Growth

  • Does carrying capacity for an area ever change? Why or why not?


Population growth rate exponential j curve

Some populations start slow and then have a burst of growth.

This is called EXPONENTIAL growth.

What shape curve does it have?

70

60

50

40

30

20

10

0

Population

0 1 2 3 4 5 6

Time

Population Growth RateExponential “J” Curve


Population growth rate exponential j curve1

What is the slow almost flat growth called?

What is the fast almost straight up growth called?

70

60

50

40

30

20

10

0

Population

0 1 2 3 4 5 6

Time

Population Growth RateExponential “J” Curve

Exponential

B

Lag

A


What is this curve called

What is this phase?

A.

What is this phase?

B.

What is this curve called?


Population growth rate logistic s curve

Some populations start slow, have a burst of growth, then level off.

This is called LOGISTIC growth.

What shape is the curve?

600

500

400

300

200

100

0

Population

0 10 20 30

Time (in days)

Population Growth RateLogistic “S” Curve


Population growth rate logistic s curve1

Logistic curves have a lag phase and an exponential phase.

Where are they on this graph?

600

500

400

300

200

100

0

A

D

Population

C

B

0 10 20 30

Time (in days)

Population Growth RateLogistic “S” Curve


Population growth rate logistic s curve2

The almost flat, slightly up/down line is called stabilization.

What letter represents stabilization on the graph?

600

500

400

300

200

100

0

A

D

Population

C

B

0 10 20 30

Time (in days)

Population Growth RateLogistic “S” Curve


Population growth rate logistic s curve3

What is carrying capacity?

What letter represents it?

Why does the population stabilize at “A”?

600

500

400

300

200

100

0

A

D

Population

C

B

0 10 20 30

Time (in days)

Population Growth RateLogistic “S” Curve


Population growth rate logistic s curve4

What will happen to a population if it goes over the carrying capacity?

What will happen to a population if it drops under the carrying capacity?

600

500

400

300

200

100

0

K carrying capacity

K

stabilization

Population

exponential

lag

0 10 20 30

Time (in days)

Population Growth RateLogistic “S” Curve


Population growth rate logistic s curve5

Population Growth RateLogistic “S” Curve

What is this?

What is this?

A.

D.

Why does it rise and fall slightly?

What is this?

B.

What is this?

C.


Natural selection and populations

Recall Darwin’s

Concepts of Natural Selection

variation exists in all species

organisms produce more offspring than can survive

competition for limited life resources

survival of the fittest (most suited to the environment)

descent with modification

Natural Selectionand Populations


Natural selection and populations1

Relate variation and offspring production to the population at B and C.

Describe competition when the population reaches A.

600

500

400

300

200

100

0

A

D

Population

C

B

0 10 20 30

Time (in days)

Natural Selectionand Populations


Natural selection and populations2

Relate survival of the fittest with the population at D.

Describe the population at D in terms of descent with modification and variation.

600

500

400

300

200

100

0

A

D

Population

C

B

0 10 20 30

Time (in days)

Natural Selectionand Populations


Natural selection and populations3

Relate the five concepts of natural selection to Graph #3.

Variation

Numbers increase

Competition

Survival of the fittest

Descent with modification

Event A

Event B

Event C

Event D

Natural Selectionand Populations


Human population

Human Population

  • What kind of curve is world population growth?


Human population1

Human Population

  • Where is the lag phase?

  • The exponential phase?


Human population2

Human Population

  • Where is the carrying capacity?


Human population3

Human Population

  • What historical event could have caused the dip at the arrow?


Human population4

Consider the Black Death Plague as an environmental change.

Describe the population after the Black Death (yellow arrow) in terms of variation and survival of the fittest.

Human Population


Human population5

Why would the industrial revolution cause a population increase?

(think in terms of FWSS and carrying capacity)

Human Population


Human population6

Human Population

  • Where do we go from here?

Children

per Woman:

High 2.5

Medium 2.0

Low 1.6


Human population7

What is the Earth’s carrying capacity?

When will we reach it?

Who will survive?

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

Human Population


Works cited

Works Cited

  • “Big Horn Sheep”, “Seabirds”. No date. Online Image. Free Stock Photos. June 15, 2004. <http://www.geekphilosopher.com/MainPage/bkgLinksPhotos.htm>


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