D2.3
Changing Populations
Overgrowth in Human Populations
• Recall, sustainability is:
– the ability for a population (or
ecosystem) to be maintained
at a certain rate or level, by
also ensures the availability of
resources in the future.
• If a human population
grows beyond its
capacity, it will
experience problems
such as:
– overcrowding
– outbreaks in disease
– water, food and
housing shortages
– pollution and waste
accumulation
Overgrowth in Human Populations
New Delhi, capital of
India
Ottawa, capital of
Canada
Pop India: 1,170,938,000 in
3,287,590 km² = 356 ppl/km2
vs.
Pop Canada: 34,108,752 in
9,984,670 km² = 3.50 ppl/km2
Growth Rates
• The two main growth rate
patterns are:
– Exponential growth
– Logistic Growth
• Exponential growth
– population growth at an
increasingly rapid rate in
proportion to the total population
size.
• Logistic (or constant) growth
– population growth that is
continuously growing and
decreasing over time, as a result of
balance within the population.
Growth Rates
• Bacteria are an example of a population that grows
exponentially
– Bacteria are single-celled organisms that reproduce by
splitting in two.
24
4 8
• the doubling time is the amount of time it takes
for a population to double in size
– For bacteria that happens in one generation. For populations
that DO NOT grow exponentially it takes considerably
longer.
Growth Rates
 a population that
experiences
exponential growth
will continue to grow
at a faster and faster
rate.
• for these populations, growth
will continue until a limiting
factor slows or stops the
population’s expansion
– in the Ancient Rome example;
limiting factors were disease, lack
of clean water, food and shelter.
– for bacteria; limiting factors would
be lack of food, increase in
temperature and presence of
toxin (antibiotics)
Growth Rates
 a population that
experiences
exponential growth
will continue to grow
at a faster and faster
rate.
Please copy the
completed graph into
your notes
• When exponential
growth is graphed, the
shape of the line is like
the letter “J”
– thus, these graphs are
also referred to as Jcurves
Factors that Support Exponential Growth
 species that are able to
grow exponentially:
◦ have short life spans
◦ reproduce often
◦ produce numerous
offspring
◦ do little to care for young
Factors that Support Exponential Growth
 exponential growth can
only occur in some
organisms, under ideal
conditions
◦ most often seen in
 micro-organisms (e.g.
bacteria)
 small animals (e.g. insects)
 certain plants (e.g. weeds)
Factors that Limit Exponential Growth
 Scarcity of resources,
such as:
◦
◦
◦
◦
food
water
living space / shelter
availability of mates
 Predation
 Disease
Population Explosions & Crashes
• a population
explosion is a sudden
exponential growth in a
population
• most
ecosystems
cannot
tolerate
exponential
population
growth for
very long…

…so the explosions are usually
followed a population crash: a
rapid drop in population size
Please copy the completed graph into
your notes
This is generally
due to the limiting
factors in the
ecosystem, acting
on the population.

Factors affecting populations
• Most populations
experience logistic growth,
– by definition, these populations
fluctuate in size, in responses
to environmental conditions:
• Factors that increase
population size
– births
– immigration (movement
into the population)
Factors affecting populations
• Most populations
experience logistic growth,
– by definition, these populations
fluctuate in size, in responses
to environmental conditions:
• Factors that decrease
population size
– deaths
– emigration (movement out
of the population)

If all four of these factors can occur in a population, it is
called an open population.
◦ If conditions prevent immigration and emigration, the population is said
to be closed
Carrying Capacity
Equilibrium
the carrying
capacity will
of a alternate
population
• While
some populations
is the maximum
number
of individuals
between
explosions
and crashes,
most will
thatancan
be sustained in an ecosystem
find
equilibrium
Carrying Capacity
• the curve for a population that is being
limited by its carrying capacity is called an
S-curve
Human Population Growth
• for most of its
history, the human
population has
been stable or
grown very slowly
• explosive growth of the human
population is linked with advancements in
agriculture, industry, science/medicine
 specifically the Industrial Revolution of
the 18th century
 living conditions improve (better
hygiene linked with higher education)
 death rate lowered due to
advancements in medicine
Human Population Growth
•
the 21st century
is the first time in
the world’s history
that the elderly will
out number the
youth
• the carrying capacity of the Earth
depends on:
 food and resource supply
 waste disposal
 pollution
 access to clean water
 distribution of populations
Human Population Growth
The current
population
of the world is about
•◦ Recall
the term
“sustainability”
7,237,851,917 (~7 billion)
The human
population
is NOT
currently
growing
in a
–growing
at an annual
rate of 1.7%,
will add
approximately
93 million
sustainable
people
/ year way.
◦ The carrying capacity of the Earth is estimated to be
around ~12 billion
 If the human population growth continues at its current rate of
growth, scientists estimate it will reach the earth’s carrying capacity
in ~ 53 years
Human Population Growth
• Recall the term “sustainability”
– Will the the human population be an S-curve…
…or a J-curve?
• PRACTICE
PROBLEMS # 7, 8,
10 & 11 (pg 484)
18-22 (pg 485)
• 2.3 Summary Q. 5
(pg 487)