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Population Growth

Factors Affecting Population Growth Rate

• 3 factors affect population growth rate:

–Number of births

–Number of deaths

–Migration

• These factors will be directly affected by the availability of resources.

Migration • Immigration—movement of

individuals into an area that has an existing population

• Emigration—movement of individuals out (exiting) of a population

• Zero growth when immigration & birth rate are EQUAL to emigration & death rate

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Did you see exponential growth in either the Paramecium lab or human population growth

activity?

Exponential growth is characterized by a J-shaped curve.

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Under ideal conditions with unlimited resources, and in the absence of disease or predation a population will grow exponentially.

Exponential growth occurs when the individuals in a population reproduce at a constant rate.

The population becomes larger and larger until it approaches an infinitely large size.

Exponential Growth

Human Population Growth Activity

• When the human population levels off, what will it have reached?

• Carrying capacity- the maximum number of individuals that a stable environment can support.

Human Population Growth Activity

• If the carrying capacity of the earth is 9 billion, what year will this number be reached?

• What will happen when the earth exceeds it’s carrying capacity?

• What factors contributed to the world’s overall population growth over the past 150 years?

• Why does a population not level off during the same year it reaches zero population growth?

Logistic growth is characterized by an S-shaped curve. It also shows the carrying capacity of the population.

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Logistic Growth

As resources become less available, the growth of a population slows or stops.

Logistic growth occurs when a population's growth slows or stops following a period of exponential growth.

Logistic growth occurs in natural populations NOT exponential. WHY?

Competitive Exclusion Principle

• No two species can occupy the same niche in the same place at the same time. WHY?

• One species will be eliminated from a community because of competition for the same limited resource.

• How did the Paramecium lab demonstrate competitive exclusion?