Science 20 Unit D

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Science 20 Unit D Living Systems

• Populations

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Populations

• Populations can grow so fast that they exhaust
  their resources.
• Examples?
• Why is this a problem? Where do we see this
  happening today?

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Some statistics National Geographic

• In 8000 B.C., only 5 million people were alive.
• By comparison, 33 million people live today in
  Canada.
• Today, the number is around 6.7 billion.
• http//www.census.gov/cgi-bin/ipc/pcwe

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The world population increased from 3 billion in
1959 to 6 billion by 1999, a doubling that
occurred over 40 years. The Census Bureau's
latest projections imply that population growth
will continue into the 21st century, although
more slowly. The world population is projected to
grow from 6 billion in 1999 to 9 billion by 2040,
an increase of 50 percent is expected to require
41 years.
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In addition to growth rates, another way to look
at population growth is to consider annual
changes in the total population. The annual
increase in world population peaked at about 88
million in the late 1980s. The peak occurred
then, even though annual growth rates were past
their peak in the late 1960s, because the world
population was higher in the 1980s than in the
1960s.
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http//www.census.gov/ipc/www/idb/ranks.html
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World Populations March 2006
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In order to study population growth, bacteria is
used it is easy to study and can imitate human
populations very well. Plus, bacteria grow and
reproduce much faster than humans, allowing us to
develop generations of data in a number of days.
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Exponential Growth

• Bacteria (like people), grow exponentially.
• When measuring exponential growth, we dont count
  by how much the population grows by each time
• we count how long it takes for the population to
  double.

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Thinking back in S20what could this similar
graph model?
This is an exponential graph of population
density of a bacteria vs. time.
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Factors that affect populations

• 4 major factors
• Number of births (natality).
• Number of deaths (mortality).
• Immigration (movement in).
• Emigration (movement out).

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Above are two population graphs what can be said
of the natality/mortality rates in these
countries?
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Natality Rates, March 2006
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Immigration sometimes faces criticism, even as
most economies are struggling to find
workers. Take a look at the graph to the right
how is this data displayed? Does anything smell
fishy to you?
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• Two types of populations
• Closed No movement in/out due to
  natural/artificial settings. Only death/births
  affect population (ex N Korea)
• Open exist in natural setting where all 4
  factors affect population size (ex Canada)

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Population explosions and crashes

• If an organism is introduced where there are no
  predators a population explosion/growth occurs.
• What happens when the food is gone? The
  population crashes!
• Example Rabbits released in Australia (1859).
• Curve shape up, then down.

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Rabbits Public Enemy 1
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Carrying Capacity

• The maximum number of individuals that can be
  sustained by an ecosystem indefinitely limited
  by disease, competition and famine.
• Instead of crashing, the population levels off at
  a stable number of organisms.
• Curve shape S curve.

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(No Transcript)
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Carrying Capacity of the Earth?
Kind of a loaded question Estimates peg it
somewhere between one and two billion (UN
population report). But opinions do vary
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http//www.youtube.com/watch?vB6JLvIxdbjQ
http//www.youtube.com/watch?vHIUyyY6L5PQfeature
fvsr
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Prof. Steve Jones, University College London
"Humans are 10,000 times more common than we
should be, according to the rules of the animal
kingdom, and we have agriculture to thank for
that. Without farming, the world population would
probably have reached half a million by now."
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Malthus

• Thomas Malthus was the first to hypothesize how
  populations grow.
• He predicted that the human population would
  crash because of shortage of resources. Why did
  this not happen?
• Do you think a population crash will occur? Why
  or why not?

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Assignment

• Skim pg 482-487
• Questions 1-6 on page 487