Download 2016-2017 Population Growrh and Urbanization

Population Growth and
Reproductive Patterns
Factor Affecting Population Size
Population Size (N)
Population
Change
=
Births
+
Immigration
–
Deaths
+
Emigration
•birth rate and death rate reported as the number
per thousand people;
•zero population growth (ZPG) occurs when births
balance deaths
Population Change
• If the birth/immigration rate are less than the
death/emigration rate than the population
decreases
• If the birth/immigration rate are greater than
the death/emigration rate than the
population increases
Density Factors and Population Growth
Dynamic characteristics of populations
• Size, number of individuals (N)
• Density (N/ area)
• Dispersion,
– uniform, clumped, random
• appropriate scale
• Age distribution,
– proportions of young,
middle-aged, old
Density Factors and Population Growth
2 Categories:
1. Density-Dependent Factors
2. Density-Independent Factors
Density Dependent
• Density-dependent
controls
• More of an effect as
population increases
• Biotic components.
• Competition
• Territoriality
• Disease,
parasitism
• Predation
• Stress responses
to crowding
Lynx and Hare
Density-Independent
• Density-independent controls
– Population size has no effect
– Abiotic components
• Drought,
• extreme temperatures,
• Light (or lack of),
• Oxygen (or shortage),
• etc.
2 Types of Population Growth
1. Exponential Growth
2. Logistic Growth
Exponential Growth
- As the population gets larger, it also grows
faster
- Unchecked growth
- J shaped curve
Logistic Growth
- Growth is determined by limiting factors
- S shaped curve
- food availability
- disease
- predators
- lack of space
- due to these factors populations
may stabilize keeping the population
at or below the carrying capacity
What is Carrying Capacity?
• Is the maximum
population a habitat
can support indefinitely
• Population exceeds it,
for long periods,
degrades its
environment and
reduces future carrying
capacity
Carrying Capacity
• The number of organisms of one species that
an environment can support indefinitely
Population Growth
• US has over 300
million people
• Growth is
determined by
biotic potential
and carrying
capacity
Reproductive Strategies
• R Strategists
 Short life span
 Small body size
 Reproduce quickly
 Have many young
 Little parental care
 Ex: cockroaches,
weeds, bacteria
Reproductive Strategies
• K Strategists
 Long life span
 Large body size
 Reproduce slowly
 Have few young
 Provides parental
care
 Ex: humans,
elephants
Survivorship Curves
• Type I individuals survive well early in life and generally live many
years. At an advanced age, the death rate increases
dramatically. Examples include large mammals.
• Type II individuals have a death rate that is relatively constant at
any age. Examples include lizards, hydra, and some small
mammals.
• Type III individuals initially have a rather low chance of
survival. Those that do survive may live to an advanced
age. Examples include many fish and other marine organisms.
Age Structure Curves
A population pyramid, or age pyramid or age picture
diagram or age structure diagram, is a graphical illustration
that shows the distribution of various age groups in a population
(typically that of a country or region of the world), which forms
the shape of a pyramid when the population is growing. It is
also used in ecology to determine the overall age distribution of
a population; an indication of the reproductive capabilities and
likelihood of the continuation of a species.
Activity: Where Do You Stand?
• Rank the following statements from 1-10;
– 1 (Strongly Disagree) to 10 (Strongly Agree)
• Be ready to take your stand and discuss your
opinions with your classmates.
• 1. Because our population will soon
be at seven billion people and
continues to grow, we need to
expand land area available for living
and growing food by cutting down
the rain forest.
 2. Without reducing rapid population
growth, it will be impossible to solve
the world’s global challenges.
 3. With seven billion people
commuting from one place to
another, drilling for more oil is
necessary to fuel more cars.
 4. In order to feed our population, we
must use pesticides, chemical
fertilizers, and genetically modified
crops to increase farm yields.
 5. With new technologies used to
gather fish, we must have
international laws to ensure seafood
is harvested sustainably.
 6. The Earth can support seven billion
people now and will be able to
support any number of human in the
future.
 7. In an effort to feed a population of
seven billion, people in developed
countries should reduce the amount
of meat they consume.
 8. Science and technology will ensure
that food production and energy
supplies keep up with the demands
of a growing population.
 9. With human population at seven
billion, we must protect endangered
species habitats by not developing on
them for any reason.
 10. There is nothing I can do to help
alleviate population pressures.
 11. Governments in countries with
fast-growing populations should
make laws to limit the number of
children that couples can have.
 12. In a real crunch, jobs are more
important than environmental
quality.
 13. With seven billion people on the
planet, water pollution is inevitable
and we should not waste money
trying to prevent it.
 14. Even though I am only one person
in seven billion, I still have a
responsibility to keep the Earth
healthy; what I do makes a
difference.
 15. Automobile makers in this
country should be required by law to
make all their vehicles fuel efficient,
even though the vehicles may
become more expensive.
 16. If China and India can each take
care of over a billion people on
relatively the same size land as the
U.S., then the U.S. should accept
immigrants until it reaches a billion
people as well.
 18. Arable land should never be used
for housing, businesses, or other
non-agricultural uses because we
need all available farmable land to
produce food.
What is Urbanization?
• The movement of
people from rural
areas to cities
• Depend on
resources outside
the city
Why are big cities growing?
• Increase in birth
rates
• Immigration
– Poor are moving
to larger cities and
away from rural
areas
How are cities growing
• Cities have grown from 2%
to 45% since 1950
• By 2050, 66% of all people
in the world will live in
urban areas
• 75% of the U.S. population
lives in urban areas
occupying 3% of the
country’s land area
Effect of Cities
• Heat Island
– The enormous
amount of heat is in
the center of the city
– 3º to 5º C (5º--9ºF)
higher than the
surrounding
countrysides
Benefits of Urban Development
• Better education
system
• Medical services
• Social Service
programs
Problems of Urban Development
• Infectious diseases
• Inadequate water
system
• Poor sewer
systems
• Exposure to
pollution