Transcript Slide 1

3.1 Population Dynamics
Crude Birth Rate (b)
The number of
births per
thousand
individuals in a
population in a
year.
Crude Death Rate (d)
The number of
deaths per
thousand
individuals in a
population in a
year.
Natural increase rate (r)
Natural Increase rate (%)= crude birth rate – crude death rate
10
Immigration and emigration is ignored!
• birth rate expressed as number of births per 1000 per year
(currently 14 in the U.S.);
• death rate expressed as the number of deaths per 1000 per
year (currently 8 in the U.S.);
• So the rate of natural increase is 6 per thousand (0.006 or
0.6%).
Although the value of r is affected by both birth rate and death rate, the
recent history of the human population has been affected more by
declines in death rates than by increases in birth rates.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
Case studies - Mexico since 1930.
The graph shows birth and death
rates in The introduction of public
health measures, such as:
better nutrition
greater access to medical care
improved sanitation
more widespread immunization
has produced a rapid decline in death
rates, but until recently there was no
corresponding decline in birth rates.
In 2010, r is 1.4%. (Data from the
Population Reference Bureau.)
Although death rates declined in all age groups, the reduction among infants and children
had — and will continue to have — the greatest impact on population growth. This is
because they will soon be having children of their own.
This situation, resulting in a rapid rate of population growth, is characteristic of many of
the poorer regions of the world.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
The Demographic Transition
Slowly declining birth rates following an
earlier sharp decline in death rates are
today characteristic of most of the lessdeveloped regions of the world.
The shift from high birth and death rates
to low birth as well as death rates is
called the demographic transition.
This graph (based on data from the Population Reference Bureau) shows that the
demographic transition began much earlier in Sweden than in Mexico and was, in
fact, completed by the end of the nineteenth century. The spike in deaths in the
interval between 1901 and 1926 was caused by the worldwide influenza pandemic of
1918–1919.
The birth rate in Sweden is now (2010) 12/1000; the death rate 10/1000, giving a rate
of natural increase (r) of 0.2%.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
Case Study – Sri Lanka
Prior to World War II, advances
in public health has been
largely limited to affluent,
industrialized countries. But
since then, improvements in
public health have been made
in many of the poorer countries
of the world — always with
dramatic effect on death rates.
In 1945, the death rate in Sri Lanka (then called Ceylon) was 22/1000.
In 1946, a large-scale program of mosquito control — using DDT — was started.
By eliminating its vector, the incidence of malaria dropped sharply.
After 9 years, the death rate dropped to 10/1000, and by 2010 was 7.
But a compensating decline in birth rates has come more slowly (19/1000 in 2010).
So by 2010 the population was increasing at an annual rate of 1.2% (12/1000/year).
At this rate the population would double in 57.5 years.
• Let's see why.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
What is exponential growth?
• The prediction that Sri Lanka will double its
population in 57.5 years is based on:
the assumption that r will remain
unchanged (which is surely false)
the mathematics of exponential growth.
• The product of growth grows itself. So the
growth of populations is a problem in
"compound interest". At the end of each year
(or whatever period you choose to use), the
base against which the rate is applied has
grown. Whatever figures you pick, as long as r
is positive, a plot of population as time
elapses will produce an exponential growth
curve like this one.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
The Population of the World
• The solid line in this graph shows
estimates of the size of the world's
population over the last two millennia.
The estimates from 1800 to 1991 are
based on more accurate data than those
before.
• The dotted line shows what would
happen if exponential growth continued
to the year 2100.
• As you can see, the world's population
has been growing exponentially (except
during the years of the black death).
How long will it continue to do so?
(Since the graph was drawn, the world's
population has reached 6.9 billion; that
is, in 2010 we are still on course.) But
can it continue indefinitely? Surely not.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
The implications of exponential growth in Human
Populations
• Think of the population density dependent
factors from the Ecology section:
Disease
––epidemics
become
more
common
LivingWaste
space
as more will
people
need
more
land to live
management
– more
people
make
as
people
have
higher
population
theremore
becomes
less
landsewage
available
fordensities;
food production
waste
– think
and
trash;
/ nature;
Look at this web site: http://tranquileye.com/clock/
Water, Water everywhere but not a
drop to drink………..
Click on the image to go to this very good website – or click here
For another summary article on the water crisis from the BBC – click here
http://news.bbc.co.uk/hi/english/static/in_depth/world/2000/world_water_crisis/default.stm
“Peak everything”
Watch these YouTube videos on exponential growth :
http://www.youtube.com/watch?v=EXd66gP53fk&feature=PlayList&p=7E8A774DA843
5EEB&playnext=1&playnext_from=PL&index=2
http://www.youtube.com/watch?v=iIwyMif5EOg
Take a look at this quite scary article about Peak oil
followed by the YouTube video:
http://www.energybulletin.net/primer.php
http://www.youtube.com/watch?v=cwNgNyiXPLk
Want to see more from Chris Martenson then check
out:http://www.chrismartenson.com/crashcourse
Fertility
• The potential for
reproduction exhibited in a
population:
1. Fertility Rate - the no. of
births per 1000 women of
child bearing age.
2. Total Fertility – the average
number of children a
woman has in her life-time.
Doubling time
• The number of years it would take a
population to double its size at its current
growth rate.
• A natural increase of 1% will allow a
population to double in 70 years.
• Other doubling times can be calculated
proportionally i.e:
Doubling time =
70
natural increase rate
Some practice questions……….
• Mexico – 1970 –
Birth rate (b)= 40/1000; Death rate (d)= 10/1000
Natural increase rate (r) = Birth rate (b) – Death rate (d)
10
3%
Doubling time =
70
% Increase rate
70 / 3%
23 years
Now try Sweden……….
• The birth rate in Sweden is now (2010)
12/1000; the death rate 10/1000, giving a rate
of natural increase (r) of 0.2%.
Doubling time of 350 years
……..or try Sri Lanka……….
• The birth rate in Sri Lanka is now (2010)
19/1000; the death rate 7/1000, giving a rate
of natural increase (r) of 1.2%.
Doubling time of 58years
Age / Sex Pyramids
•
Aside from the total size, the most important demographic characteristic of a population is its
age and sex structure, or the proportion of people at each age, by sex. The age-sex structure
determines potential for future growth of specific age groups, as well as the total population.
For these reasons, the age structure has significant government policy implications. A
population of young people needs a sufficient number of schools and, later, enough jobs to
accommodate them. Countries with a large proportion of older people must develop retirement
systems and medical facilities to serve them. Therefore, as a population ages, needs change
from childcare and schools to jobs, housing, and medical care. Read on at………….
http://www.prb.org/Educators/TeachersGuides/HumanPopulation/Change.aspx
China
• China had an extreme
youth bulge until the
1960s, when it sharply
curbed partly as an
effect of the one-child
policy.
• Compare this with the
population pyramid of
the USA which was
bulging until the 1960s
and has steadily slimmed
since.
• Take a look at gender
balance in both………
http://en.wikipedia.org/wiki/Demographic_transition
Demographic Transition Models
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Stable pyramid - A population pyramid showing an unchanging pattern of fertility and mortality.
Expansive pyramid - A population pyramid showing a broad base, indicating a high proportion of children, a rapid rate
of population growth, and a low proportion of older people. This wide base indicates a large number of children. A
steady upwards narrowing shows that more people die at each higher age band. This type of pyramid indicates a
population in which there is a high birth rate, a high death rate and a short life expectancy. This is the typical pattern
for less economically developed countries, due to little access to and incentive to use birth control, negative
environmental factors (for example, lack of clean water) and poor access to health care.
Stationary pyramid - A population pyramid typical of countries with low fertility and low mortality, very similar to a
constrictive pyramid.
Constrictive pyramid - A population pyramid showing lower numbers or percentages of younger people. The country
will have a greying population which means that people are generally older, as the country has long life expectancy, a
low death rate, but also a low birth rate. This pyramid has been occurring more frequently, especially when immigrants
are factored out, and is often a typical pattern for a very developed country, a high over-all education and easy access
and incentive to use birth control, good health care and a low number to no negative environmental factors.
http://en.wikipedia.org/wiki/Demographic_transition
•
Read More:
http://en.wikipedia.org/wiki/Demograp
hic_transition
The demographic transition (DT) is a model
used to represent the transition from high birth
and death rates to low birth and death rates as
a country develops from a pre-industrial to an
industrialized economic system. The theory is
based on an interpretation of demographic
history developed in 1929 by the American
demographer Warren Thompson (1887–
1973).[1] Thompson observed changes, or
transitions, in birth and death rates in
industrialized societies over the previous 200
years. Most developed countries are in stage 3
or 4 of the model; the majority of developing
countries have reached stage 2 or stage 3. The
major (relative) exceptions are some poor
countries, mainly in sub-Saharan Africa and
some Middle Eastern countries, which are poor
or affected by government policy or civil strife,
notably Pakistan, Palestinian Territories, Yemen
and Afghanistan.[2]
Questions on Demographic Transition Model:
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•
Look back at the ‘Birth rate/death rate’ graphs for Mexico, Sweden and Sri Lanka.
Identify which stage in the Demographic Transition Model is each country in the
following years:
Country
Date
Stage
Mexico
1970
2
Sri Lanka
1910
1
Mexico
1984
3
Sweden
1984
4
Look at this great animation of Canada’s Age sex population graphs from 1901 to the
present day. Try to identify about when Canada goes through each of the stages in
the DTM. http://www12.statcan.ca/english/census01/products/analytic/companion/age/cda01pymd.cfm
Stage
Date
1
1900s
2
1920 - 1960
3
1961 - 1975
4
1976 - 1990
5
1991 - Present
Predicting Populations
• Look at this great website- explore!
http://www.census.gov/ipc/www/idb/informationGateway.php
• Find out :
Who are Malthus (1766-1834) and Boserup
(1965)?
Compare their predictions for what will happen
to populations and why. Which do you think is
most likely?
Looking Ahead
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Exponential growth cannot continue indefinitely. If the
current world value for r (1.2%) remains unchanged, the
world population would grow from its current 6.9 billion to
9.5 billion over the next 40 years (2050).
Could the earth's resources sustain such a population?
If not, how large a human population can live decently on
this planet?
Some demographers (students of population) say we have
already exceeded the number. Others say the earth can hold Total Fertility Rate (TFR)
The total fertility rate is the average
billions more.
number of children that each woman
Whatever the case, there are grounds for some optimism
will have during her lifetime. The TFR
is an average because, of course,
about future population growth.
some women will have more, some
The world value for r peaked around 1990 and has declined fewer, and some no children at all.
Theoretically, when the TFR = 2, each
since. This is a reflection of the decline in total fertility rates pair of parents just replaces itself.
(TFRs) in undeveloped countries, presumably as the various Actually it takes a TFR of 2.1 or 2.2 to
replace each generation — this
factors involved in the demographic transition take hold, e.g., number is called the replacement rate
–
–
–
–
improved standard of living
increased confidence that your children will survive to maturity
improved status of women
increased use of birth control measures
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
— because some children will die
before they grow up to have their own
two children. In countries with low life
expectancies, the replacement rate is
even higher (2.2–3).
The projection of future TFRs in the graph above (from the Population Reference
Bureau) predicts that the less developed countries of the world will reach
replacement fertility around the year 2020. In fact, they will probably reach it
sooner because by 2010 the world TFR has dropped to 2.5. Even so, will the
world reach zero population growth (ZPG) then?
• This graph (based on data from the UN LongRange World Population Projections, 1991) gives
5 estimates of the growth of the world
population from now until 2150, assuming that
TFRs decline from the 1991 value of 3.4 to the
values shown.
• A value of 2.06 will produce a stable population
of about 11.5 billion.
• A value 5% below that (1.96) will cause the
population to drop back to close to its present
value (6.1 billion) while
• a value of only 5% above (2.17) would produce a
population of over 20 billion and still rising.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html
To conclude:
The several agencies that try to predict future
population seem to be moving closer to a
consensus that:
• the world population will continue to grow
until after the middle of this century
• reaching a peak of some 9.5 billion (up from
today's 6.9 billion) and then
• perhaps declining in the waning years of this
century.