Download Population Growth

Populations
How do they change over time?
What is a population and how is it
measured?
• POPULATION: A group of
organisms that belong to
the same species living in
the habitat at the same
time.
• GROWTH RATE = Births –
Deaths
– Immigration: moving
INTO an area
– Emigration: EXITING an
area
How are populations distributed?
POPULATION DENSITY:
Number of individuals per
unit area.
CLUMPED (in groups)
RANDOM (all over)
UNIFORM (spread evenly)
How do populations grow?
• Exponential Growth (J curve): population increases
rapidly very quickly only after a few generations
Exponential growth
Peak population
size
Rapid decline
Steady population
size
Steady population
size
Grow forever? Micro-organisms can if given enough nutrients and space!
How do populations grow?
• Logistic Growth (S curve): starts as exponential growth
with limiting factors and levels off (due to carrying
capacity)
Carrying capacity
• Carrying Capacity
is the MAXIMUM
number of
individuals an
environment and
its resources can
support
Time (hours)
As resources become less available the growth of a population slows or stops.
Limiting factors prevent MOST populations from growing forever.
What factors limit population growth?
• Limiting Factors control the growth of a
population
– Available resources (food, space, mates)
– Competition, predation, parasitism,
disease
– Natural disasters, unusual weather
Limiting factors determine the carrying
capacity for a species.
What factors limit population growth?
• Environmental changes (ex. drought)
• Other species
– Predators, prey, competitors
– Lynx and snowshoe hare example
How is the human population
growing?
12
Human Population (Billions)
11
2100
10
9
Old
Stone
7 Age
8
New Stone Age
Bronze
Age
Modern
Age
Iron Middle
Age Ages
6
2000
Future
5
4
1975
3
1950
2
1
Black Death—The Plague
1900
1800
1+ million7000 6000 5000 4000 3000 2000 1000 A.D. A.D. A.D. A.D. A.D. A.D.
years B.C. B.C. B.C. B.C. B.C. B.C. B.C. 1 1000 2000 3000 4000 5000
• Earth - 5 Billion
Years
• Multi-cell Biota
- 600 Million
Years
• Human Beings
~ 2 Million Years
• Human
Population
Growth into
Billions- Last 200
years
What’s Behind the Human Population
Explosion?
• Three Factors
•
– Fertility
– Infant Mortality
– Longevity
• Animal
Domestication and
Agriculture
– Provided for a few
to feed many
Industrial Revolution
– Growth of Cities and
Infrastructure
•Water
•Energy
•Transportation
– Increased Productivity
– Nutrition
– Sanitation
– Medicine
How are humans affecting the
environment?
• Limited Resources
– Land, food, water
• Agriculture
• Industries
• Ecosystem Goods
– Renewable
– Nonrenewable
• Desertification &
Deforestation
• Water pollution
• Biological magnification
• Air pollution
• Acid rain
• Habitat Fragmentation
• Introduced Species
 What is the size of YOUR
ecological footprint?
(take the quiz online!)
Any Questions?