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Biology
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5-1 How Populations Grow
Photo Credit: © Frans Lanting/Minden Pictures, Inc.
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3. Characteristics of Populations
What characteristics are used to describe a population?
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4. Characteristics of Populations
Three characteristics of a population:
geographic distribution
population density
growth rate
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Population Growth
Population Growth
Three factors can affect population size:
the number of births
the number of deaths
the number of individuals that enter or leave the population
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. Emigration- the movement of individuals out of an area, can cause a population to decrease in size.
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Exponential Growth
Types of Growth
Exponential Growth: If unlimited resources, a population will grow exponentially.
Logistic Growth: As resources become limited, the growth of a population slows or stops. .
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Carrying Capacity
Largest numbers of individual a given environment can support
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Limiting Factors
Limiting Factors
a factor that causes population growth to decrease.
Can be
Density dependent – factor depends on number of individuals in area
Density Independent – factor is not affected by number of individuals in area
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10. Density-Dependent Factors
Density-dependent limiting factors include:
competition
predation
parasitism
disease
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11. Density-Dependent Factors
Competition
Compete for food, water space, sunlight and other essentials.
Competition can occur within a species or between species
- Could result in species evolving to occupy new niches
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12. Density-Dependent Factors
Predation
Predator-prey relationship: Populations in nature are often controlled by predation.
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13. Density-Dependent Factors
Wolf and Moose Populations on Isle Royale
The relationship between moose and wolves on Isle Royale illustrates how predation can affect population growth. In this example, the moose population was also affected by changes in food supply, and the wolf population was also affected by disease.
Moose Wolves
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14. Density-Independent Factors
Density-independent limiting factors affect all populations in similar ways, regardless of the population size.
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15. Density-Independent Factors
Examples of density-independent limiting factors include:
Weather, natural disasters, and seasonal cycles
Certain human activities—such as damming rivers and clear-cutting forests
Environmental conditions
- climate, pollution
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Is humans hunting deer a density dependent or independent factor?
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