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Human Population and the
Environment
• Human population is growing rapidly and
steadily.
• Ultimately, there can be no long-term solutions to
environmental problems unless the human
population stops increasing.
• Countries with a high standard of living
(developed countries) have moved more quickly
to a lower birth rate than have countries with a
low standard of living.(developing countries).
A brief history of human population
growth
• 1.) In the earliest part of human history-probably
less that a few million hunters and gatherers
• 2.) The rise of agriculture allowed for a much
greater density of people and the first major
increase in human population.
• 3.) The industrial revolution, with improvements
in healthcare and food supply led to the most
rapid increase in population.
• 4.) Today, the rate of population growth has
slowed in industrialized nations but continues to
increase in poorer, less developed nations.
Carrying Capacity
• Carrying capacity-the maximum population of
a particular species that a given area of
habitat can support over a given period of
time.
• A sustainable supply of resources defines the
carrying capacity for a particular population in
a particular environmental system.
Human Population and the
Environment
Basic definitions:
Population-a group of individuals of the same
species living in the same area or
interbreeding and sharing genetic
information.
Species-made up of populations
Human Population and the
Environment
• Five Key Properties of any Population are:
• 1.) Abundance-the size of any population now, in the past
and in the future
• 2.) Birth rates
• 3.) Death rates
• 4.) Growth rates
• 5.) Age structure
• Demography-is the statistical study of human populations.
• Population Dynamics-the general study of population
changes over time.
Linear vs. Exponential
growth rates
• Growth rates of
populations can be
characterized by two
different growth rates:
linear and exponential.
Linear Growth
• Linear growth occurs at
a contant rate. An
example would be if
your employer
increases your salary by
exactly $1000.00 every
year. This would result
in a gradual increase in
your salary.
• We call it linear because
the resulting graph
would be a straight
line.a
Exponential growth
• Most species are
capable of increasing
their population at an
exponential rate. An
example of exponential
growth would be if a
population of mice
increased their number
by 10% each month.
• In this case the resulting
graph would be a sharp
upward curve
illustrating the
population explosion of
mice.
PICK AN OPTION FOR YOUR SUMMER
JOB(50 days):
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•
•
•
•
Option 1:
Day 1: $0.01
Day 2: $0.02
Day 3: $0.04
Day 4: $0.08
•
•
•
•
•
Option 2:
Day 1: $100.00
Day 2: $100.00
Day 3: $100.00
Day 4: $100.00
Outcome (summer job)
• $100.00 job:
• Day 20: $2000.00 total
• Day 50: $5000.00 total
for the summer
• $.01 job:
• Day 20: $10,486 total
• Day 50: $11.259 trillion
dollars total for the
summer
Exponential growth (j-curve)
Human Population Growth
Can a population continue to
experience exponential growth
indefinitely?
Logistic Growth (s-curve)
K=carrying capacity
Carrying capacity
• As a population increases in size, the same
resources must be shared by a greater and
greater number of individuals. The decreasing
supply of resources may lower the population’s
birth rate , increase its death rate, or both-until
births and deaths are in balance.
• At that point of balance, and as long as the
resource supply remains constant, the population
should stabilize at some equilibrium size.
• This is the carrying capacity
Population Age Structure
• Population age structure graphs show the
proportion of the population of each age.
• The age structure of a population affects
current and future birth rates, death rates,
and growth rates, has an impact on the
environment, and has implications for current
and future social and economic conditions.
Age Structure
Limiting Factors
• Limiting factor-anything preventing the growth of
a population
• Examples of things that may be limiting factors:
• Space
• Food
• Climate and weather
• Cover
• Disease
• Human activity
• shade
Density-dependent limiting factors
• Limiting factors that are dependent on the size
and density of a population
• Examples include disease, competition, and
predation
Density-independent limiting factors
• Limiting factors that effect all members of a
group equally regardless of the population
density
• Examples-limited food supply, natural
disasters, environmental stress
What is the human carrying capacity
of the Earth?
• How many people can live on the Earth at the
same time?
• The answer depends on what quality of life
people desire and are willing to accept.
• Estimates of how many people the planet
will support range from 2.5 billion to 40
billion. (currently 6.6 billion)