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Population Growth
Copyright Pearson Prentice Hall
Factors Affecting Population
Growth Rate
• 3 factors affect population growth rate:
–Number of births
–Number of deaths
• These factors will be directly affected
by the availability of resources.
• Immigration—movement of
individuals into an area that has an
existing population
• Emigration—movement of
individuals out (exiting) of a
• Zero growth when immigration &
birth rate are EQUAL to emigration &
death rate
Exponential growth is characterized by
a J-shaped curve.
Did you see exponential growth in either the
Paramecium lab or human population growth
Copyright Pearson Prentice Hall
Exponential Growth
Under ideal conditions with unlimited
resources, and in the absence of disease or
predation a population will grow
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.
Copyright Pearson Prentice Hall
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
• 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
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?
Copyright Pearson Prentice Hall
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?