Population Ecology

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Zero population growth = High birth rate – High death rate

Zero population growth = Low birth rate – Low death rate

The demographic transition is the move from the first state toward the second state.

Slide 45

Age Structure

One important demographic factor in present and future growth trends is a country’s age structure.

Age structure is the relative number of individuals at each age.

Age structure diagrams can predict a population’s growth trends.

They can illuminate social conditions and help us plan for the future.

Slide 46

Age-structure pyramids for the human population of three countries

Rapid growth

Afghanistan

Male

Female

Age

Age

Male

Female

Slow growth

United States

Male

Female

No growth

Italy

85+

80–84

75–79

70–74

60–64

65–69

55–59

50–54

45–49

40–44

35–39

30–34

25–29

20–24

15–19

0–4

5–9

10–14

85+

80–84

75–79

70–74

60–64

65–69

55–59

50–54

45–49

40–44

35–39

30–34

25–29

20–24

15–19

0–4

5–9

10–14

10

10

8

8

6

6

4

4

2

2

0

Percent of population

Percent of population

Percent of population

6

6

4

4

2

2

0

8

8

6

6

4

4

2

2

0

8

8

Slide 47

Estimates of Earth’s Carrying Capacity

How many humans can the biosphere support?

The carrying capacity of Earth for humans is uncertain.

The average estimate is 10–15 billion.

Slide 48

Limits on Human Population Size

The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation.

It is one measure of how close we are to the carrying capacity of Earth.

Countries vary greatly in footprint size and available ecological capacity.

Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes.

Slide 49

Review: Population Growth Curve

Number of generations

K = carrying capacity

Population size (N)

rmax N

dN

dt

=

K – N

K

Slide 50

You should now be able to:

Define and distinguish between the following sets of terms: density and dispersion; clumped dispersion, uniform dispersion, and random dispersion; life table and reproductive table; Type I, Type II, and Type III survivorship curves; semelparity and iteroparity; r-selected populations and K-selected populations.