How Populations Grow

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How Populations Grow
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Three Things That Affect Population Growth

• Number of Births
• Number of Deaths
• Migration
• Movement of animals from one place to another

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Types of Migration

• Emigration
• Movement of individuals out of an area
• Immigration
• Movement of individuals into an area occupied by
  an existing population

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Equation for Population Growth

• Birth Rate Immigration Death Rate - Emigration

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Exponential Growth

• When individuals in a population grow at a
  constant rate
• Example
• When a population has unlimited resources

Population size
Time
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Limiting Factors

• A condition that causes the growth of a
  population to decrease
• Examples
• predation, disease, natural disasters, food
  shortages, etc.

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Carrying Capacity

• Largest number of individuals in a population
  that a given environment can support

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Logistic Growth

• When a populations growth rate stops or slows
  after a period of exponential growth
• Example
• When a population reaches carrying capacity

Logistic Growth Curve
K carrying capacity of environment
K
Optimal yield ( 1/2 K)
Time (t)
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Comparing Exponential and Logistic Growth
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Limits to Growth

• Limiting Factor
• any factor that limits the size of a population
• Examples
• Predation, disease, natural disasters, food
  shortage, etc.

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Population Density

• Number of a particular organism per a specific
  area
• Examples
• of deer in a 1 acre forest
• of people in Bloomington-Normal
• of students in this classroom

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Density-Dependent Factors

• A limiting factor that depends on a populations
  size
• Examples
• Competition
• Predation
• Parasitism and Disease

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Competition

• When two organisms compete over the same limited
  resource

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Predation

• When one organism captures and feed on another
  organism

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Parasitism and Disease

• When a parasite or disease needs close contact to
  be spread from organism to organism
• West Nile Disease

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Density-Independent Factors

• A limiting factor that affects a population in
  similar ways regardless of the populations size
• Examples
• Weather (Seasonal Cycles)
• Human Activities
• Natural Disasters

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Weather (Seasonal Cycles)

• Extreme Cold or Heat
• Winter Frost
• Heavy Rainfall

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Human Activities

• Deforestation
• Hunting
• Buildings and Roads

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Natural Disasters

• Hurricanes, Tornados, Flooding
• Earthquakes, Mudslides, Forest Fires