Biology
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5-1 How Populations Grow
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Characteristics of Populations
What characteristics are used to describe a population?
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Characteristics of Populations
Characteristics of Populations
Three important characteristics of a population are its:
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Characteristics of Populations
Geographic distribution, or range, describes the area inhabited by a population.
Population density is the number of individuals per unit area.
Growth rate is the increase or decrease of the number of individuals in a population over time.
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Population Growth
What factors affect population size?
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Population Growth
Population Growth
Three factors can affect population size:
A population can grow when its birthrate is greater than its death rate.
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Population Growth
Immigration, the movement of individuals into an area, is another factor that can cause a population to grow.
Populations can increase by immigration as animals in search of mates or food arrive from outside.
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Population Growth
Emigration, the movement of individuals out of an area, can cause a population to decrease in size.
Emigration can occur when animals leave to find mates and establish new territories.
A shortage of food in one area may also lead to emigration.
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Exponential Growth
What are exponential growth and logistic growth?
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Exponential Growth
Exponential Growth
Under ideal conditions with unlimited resources, 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.
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Exponential Growth
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Exponential Growth
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Logistic Growth
Logistic Growth
In nature, exponential growth does not continue in a population for very long.
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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.
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Logistic Growth
Logistic growth is characterized by an S-shaped curve.
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Logistic Growth
Carrying Capacity
The largest number of individuals of a population that a given environment can support is called its carrying capacity.
When a population reaches the carrying capacity of its environment, its growth levels off. The average growth rate is zero.
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Population density is the number of individuals
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When the birthrate of a population exceeds its death rate, the population
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An S-shaped curve on a graph of population growth is characteristic of
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Exponential growth in a population slows down or stops as
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Exponential growth rate means that each new generation of a population
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