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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.
Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall
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?