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How Populations Grow
Photo Credit: © Frans Lanting/Minden Pictures, Inc.
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2. Characteristics of Populations
Three important characteristics of a population are its:
geographic distribution
density
growth rate
# / unit area
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Population Growth
Population Growth
Four factors can affect population size & thus growth rates:
Natality (the number of births)
Mortality (the number of deaths)
Immigration (the number of individuals that enter the population)
Emigration (number of individuals that leave the population)
When can a population grow then? When will a population decrease in size?
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Exponential Growth
Under ideal conditions with unlimited resources, a population will grow exponentially. J-Shaped curve
Exponential Growth
In the presence of unlimited resources and in the absence of predation and disease, a population will grow exponentially. Both hypothetical graphs show the characteristic J-shape of exponential population growth.
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Logistic Growth
Logistic growth is characterized by an S-shaped curve. What causes this type of growth?
What?
Why?
This graph shows the S-shaped curve of logistic growth. As resources become less available, the population growth rate slows or stops. The growth of this population has leveled off at its carrying capacity.
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Limits to growth
Density Dependent Factors:
differ with the biome/environment
Amount food
Disease
Competition
Parasites
Versus Density-Independent:
Abiotic factors
Habitat disruption
Which type of populations more prone to density-dependent factors? Density –independent?
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Predatory Prey cycles
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