Populations

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Populations
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• Population density the number of individuals
  per unit area.
• Examples
• 33 oak trees per acre
• 5 goldfish per aquarium
• 2 bears per square kilometer

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• Population size is affected by
• Births
• Deaths
• Immigration
• Emigration

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Types of growth

• Exponential growth occurs when individuals in a
  population reproduce at a constant rate
• J shaped curve

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Exponential growth graph
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• Populations will grow exponentially when there
  are unlimited resources.

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• Logistic growth occurs when a populations growth
  slows or stops following a period of exponential
  growth.

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• Resourses become less available
• S-shaped curve of graph

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Logistic growth graph
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• Carrying capacity is the largest number of
  individuals an environment can support.

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Limits to Growth

• A limiting factor is something that causes
  population growth to decrease.

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• Limiting factors that depend on population size
  are called density dependent.
• Examples disease, predation, competition,
  parasitism, waste build-up,

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Like competition
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• Populations are often kept in check by the
  predator-prey relationship

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Lynx and hare populations
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• Density independent limiting factors affect all
  populations in similar ways.
• Examples are weather and climate extremes

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Density independent example weather
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Or climate extremes
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Effects of Pollution on Ecosystems

• Air resources cities produce smog, a pollutant
  from the burning of fossil fuels that can cause
  health problems
• -acid rain nitric and sulfuric acids with a
  high pH which can kill plants and animals

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Formation of Acid Rain
Chemical Transformation Nitric acid Sulfuric acid
Condensation
Emissions to Atmosphere Nitrogen oxides Sulfur
dioxide
Dry Fallout
Precipitation Acid rain, fog, snow, and mist
particulates, gases
Industry
Transportation
Ore smelting
Power generation
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• Pollution DDT, a pesticide, became more
  concentrated as it moved up the food web
  biological magnification

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Biological Magnification of DDT
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• Ozone is a gas made up of molecules that consist
  of 3 oxygen atoms
• Antarctica has a hole in the ozone layer that
  has grown larger over the past 20 years

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Causes of ozone depletion include Aerosol sprays
that contain chlorofluorcarbons (CFCs), the
coolants in air conditioners and production of
plastic foams
CFCs are banned in US