Population Ecology

Page
6

(thousands)

Number of hares

(thousands)

160

120

80

40

0

1850

1875

1900

1925

Year

9

6

3

0

Slide 38

Hypothesis 1: The hare’s population cycle follows a cycle of winter food supply.

If this hypothesis is correct, then the cycles should stop if the food supply is increased.

Additional food was provided experimentally to a hare population, and the whole population increased in size but continued to cycle.

No hares appeared to have died of starvation.

Slide 39

Hypothesis 2: The hare’s population cycle is driven by pressure from other predators.

In a study conducted by field ecologists, 90% of the hares were killed by predators.

These data support this second hypothesis.

Slide 40

Hypothesis 3: The hare’s population cycle is linked to sunspot cycles.

Sunspot activity affects light quality, which in turn affects the quality of the hares’ food.

There is good correlation between sunspot activity and hare population size.

The results of all these experiments suggest that both predation and sunspot activity regulate hare numbers and that food availability plays a less important role.

Slide 41

Immigration, Emigration, and Metapopulations

Metapopulations are groups of populations linked by immigration and emigration.

High levels of immigration combined with higher survival can result in greater stability in populations.

Slide 42

The human population is no longer growing exponentially but is still increasing rapidly

No population can grow indefinitely, and humans are no exception.

The human population increased relatively slowly until about 1650 and then began to grow exponentially.

Though the global population is still growing, the rate of growth began to slow during the 1960s.

Most of the current global population growth is concentrated in developing countries.

Slide 43

Human population growth

8000

B.C.E.

4000

B.C.E.

3000

B.C.E.

2000

B.C.E.

1000

B.C.E.

0

1000

C.E.

2000

C.E.

0

1

2

3

4

5

6

The Plague

Human population (billions)

7

Slide 44

Regional Patterns of Population Change

To maintain population stability, a regional human population can exist in one of two configurations: