Transcript Population - out of control

Population
- out of control
Lecture1
Frontiers in Biology
www.drdulai.com/csustan
Some material from
http://www.globalchange.umich.edu/globalchange2
/current/lectures/human_pop/human_pop.html
Outline for today
• Population Lecture
• Break
• Population Video (56 minutes)
• Break
• Group discussions and question
formulation towards exams
Overview
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A. Population of what?
B. Human population milestones
C. Major eras of human history
D. Population growth in historical perspective
E. Bacterial growth
F. Easter Island example
Population - which
population?
• Most are equating the term population with that of
the entire human race
• However, one could apply the term to any
community of individuals
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Plants
Bacteria
Polar Bears
Dogs in England
• But, you would be right in this instance. We are
going to explore just human population growth
Man evolves
• According to the latest theories, man
evolved from a common man/chimp
ancestor some 5 million years ago in
Africa
• Ancient man split into a number of
species that came and went
• Around 200,000 years ago he began his
migration ‘Out of Africa’
Major Milestones in Human
Population Numbers
Number
1 Billion
2 Billion
3 Billion
4 Billion
5 Billion
6 Billion
6.675 Billion
7 Billion
Year Attained
1830 (5 million years)
1927 (97 years)
1960 (33 years)
1974 (14 years)
1987 (13 years)
1999 (12years)
2007
2008 (9 years?)
Major eras in human history
• Pre-agricultural era (beginning~8000 B.C.)
• Relied on what could be caught
• Agricultural era (~8000 B.C. - 1750)
• Began to settle down and harvest food
• Industrial era (1750 - present)
• Technology brought food to the table
The human growth curve
• This curve is said to be a “J” curve because it looks like the letter J!
• Wars and plagues have little impact on
the upward slope of this curve!
• New people are entering the world at
about one every 3 seconds now!
• Of the 6.6 billion people
• Half live in poverty
• One in five are severely undernourished
• The rest are living well!!!
• Also, half now live in urban areas
How fast can populations
grow?
• We can learn from microbiology…
• If we inoculate a flask of broth with a
single bacteria at midday
• Then, at 12:20 there will be two bacteria (because this bacteria can divide every
20 minutes)
• At 1:00 pm there will be 8
• At midnight there will be 68,719,476,736
(over 68 billion cells)
Bacterial grow rates
• Remember that these bacteria are growing
under ideal conditions
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Each cell always divides into two others
There is no death of any cell
There is always food for the cells
There is always space for the cells to grow
We would expect the population of our flask to
take over the entire planet very quickly
thereafter!
Something is going to prevent this. What?
But first…
• Easter Island example
Real Example of Human
Population Woes
• In 1722, on Easter morning, an English explorer
landed on Easter Island in the Pacific
• He found a few hundred hungry people hiding in caves
• He saw no trees and burned grasslands
• He saw 100’s heavy rock statues lined up on the shores
• Cpt. James Cook landed on the same island two years
later - he saw 4 canoes and the statues tipped over on
spikes
• What happened here?
Easter Island Paradise
• The island is just 165 sq km in size
• Around 1600 years ago settlers from other
Pacific islands came to this paradise
• Dense forest and fertile soils
• Built canoes from large trees and cooked fish with
the wood
• Cleared forest to plant crops
• Had many children
Paradise gone!
• Mid 1400’s - 10,000 to 15,000 were living on
the island
• Crop yields had declined
• Fish had vanished from costal waters
• Erosion and harvesting had depleted the soil
• All birds had been eaten
• People were raising rats as food
• They erected stone symbols to the Gods
Paradise lost!
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By 1550’s
No one fished offshore
No one built canoes - no suitable trees
No fire wood remained, as all the trees
were felled
• They then turned to their last source of
protein • each other - cannibalism!
Decline
• The government collapsed
• Small gangs began to fight each other
• They burned grasslands to prevent
surprise attacks and began hiding in
caves
• Winners ate losers
• They toppled each others statues onto
spikes
Lessons learnt
• The Easter Island society flourished when
resources were abundant - “J” curve
• That same society fell apart when the
resources became limiting
• The lesson here is that all populations are
governed by the same principles of growth
and sustainability no matter how large or
small, or who
• ECOLOGY
Back to our bacteria
• The bacteria in our flask are no different
• Let the flask equate to Easter Island
• The broth is the food supply
• The bacteria are the people
• When we left them they were following what is
called the “j” growth curve - everything is great!
• Eventually something has to give
• The bacteria can no longer grow exponentially
• Their growth will follow the following curve as time
passes…
Population Change
• If the number of deaths is balanced by the
number of births then there is no net change in
the size of the population
• If births exceed deaths = population increases
• If the deaths exceed births = population
declines
• The above assumes that there is no migration of
individuals into or out of the community.
Exponential growth
• As long as the rate of births is greater
than the rate of deaths the population
will grow exponentially
• As we know from models, no population
can maintain the exponential growth
curve indefinitely, and that would
include the human population
Human births
• We now know that there are 4 factors governing
population size;
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Fertility (Birth rates)
Mortality (Death rates)
Beginning population size
Time
• Current human growth rate is ~1.3% per year = we
are adding ~90 million new babies to the planet
each year
• It has been higher (1965-1970 it was 2.1%)
• We need to reduce fertility globally - it takes time!
Differing fertility rates
Demographic Transition
• Developed countries have undergone a
process called Demographic Transition where their population growth has
stabilized
• Developing countries of the World have
not reached this point yet
• What is the demographic transition…
Medicine
Hygiene
Agriculture
Urbanization
Migration to US
Human population growth
• We, as a whole, are growing at an
exponential rate
• What will give out first?
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Food
Water
Space
Environment
Lack of other resources
Interlinked
• We need space to grow food, but we also
need that same space for living
• We need fresh water to drink, but we also
need that water for irrigation
• We need a healthy environment but we are
polluting the same with our self centered
practices
• Data show that the rate of fertility and
development are linked… this may be the
silver lining
When will the human race hit
the stationary phase?
• Human behavior and practices need to
change or we will have to deal with the
stationary phase shortly
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Disease
Shortages (famine)
War
Remember the Alamo Easter Island!!!
When will the human race hit
the stationary phase?
• One can use population-age pyramids
to estimate future growth rates
What is the future?
• The video addresses this and has some
answers.
• Each student needs to watch and answer the
following questions,
• Which is the population of the US today?
• Which three countries did the video focus upon?
• How many children did the wife of the Raja (Shah
Jahan) who built the Taj Mahal have?
• Remember the shape of the population
pyramid for each country mentioned please
for the discussion to follow