Ecology Part II

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Ecology (Part II)
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Population Growth

• How Fast Do Populations Grow?

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Types of Growth

• linear growth straight line growth, for every
  unit increase on the x axis, there is an equal
  increase in the value on the y axis. In nature,
  populations do not grow in this manner.

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Types of Growth

• exponential growth occurs in populations where
  the population grows at an increasing rate.
• Populations in nature may grow exponentially
  when organisms occupy a new environment and
  limiting factors have almost no affect on them.

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Start out with slow growth.
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Get the picture?!
End with exponential numbers.
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You end up with a J-shaped growth curve, or an
exponential growth curve.
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However

• no population can continue to grow exponentially
  indefinitely.

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There will always be limiting factors.

• Availability of food

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There will always be limiting factors.

• Availability of food
• Disease

Courtesy of the disease called AIDS.
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There will always be limiting factors.

• Availability of food
• Disease
• Predators

SorryI had to
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There will always be limiting factors.

• Availability of food
• Disease
• Predators
• Lack of space

• Etc

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Types of Growth

• logistic growth an S shaped growth curve,
  where the population eventually levels off at the
  carrying capacity of the environment.
• The population starts growing at a very fast
  rate but environmental limiting factors start
  having an effect on the rate of population growth
  and the rate of growth slows down until the rate
  of growth reaches zero.
• At this point the number of births in the
  population is equal to the number of deaths and
  the population is at the carrying capacity of the
  environment.

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Carrying Capacity

• The number of organisms of one species that an
  environment can support indefinitely.

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Logistic Growth
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The Effects of Environmental Factors on
Population Growth
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Environmental Factors

• Predation predators control their prey species
  in a predator-prey interaction.
• The population of the prey organisms influences
  the numbers of predators and the number of
  predator organisms affects the number of prey
  species.

• Competition within a species of organisms, they
  compete for food, water, shelter, and territory.
  
• When numbers of organisms are below the carrying
  capacity, there is little competition. As the
  population approaches the carrying capacity,
  competition becomes greater and has more of an
  affect on the population.

• Crowding when species are crowded, more stress
  occurs. This may result in increased aggression,
  decreased parental care, decreased fertility, and
  decreased resistance to disease.

All of these factors tend to decrease population
size.
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The Human Population

• Factors that are affecting its growth.

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Human Growth Rate

• The human population growth rate prior to 1600
  was about zero.
• After 1600, the population started to grow at a
  faster rate.
• The growth curve is exponential and is going
  almost straight up at the present time.

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Human Growth Since 1600

• The most probable cause for the tremendous
  increase in growth rate is a drastic decrease in
  the death rate without a corresponding decrease
  in birth rate.
• The decrease in death rate was primarily due to
  decrease in disease and healthier living
  conditions.

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Human Growth Since 1600
Emigration-movement of individuals from a
population
Immigration-movement of individuals into a
population

• Populations in countries that have many young
  individuals increase faster than those that have
  the same number (percent) of individuals of all
  ages.
• Immigration and emigration have an effect on the
  population size of counties.

Russians immigrants at Ellis Island in 1910.