Transcript Population and Human Impact

All living organisms are limited by
factors in the environment
CHAPTER 3.1 & 4.1
POPULATION ECOLOGY
In Chapter 2, you learned that
organisms depend on one another for
survival. You also learned about
abiotic factors and that abiotic factors
affect individual organisms.
How, then, might these factors affect
communities and populations?
CHAPTER 2
REVIEW TERMS
 Population
is a group of
individuals of the same type (or
species)
 Species is a group of
organisms that can interbreed
and produce fertile offspring
Population growth = an increase in the size of a
population over time
 Birth rate greater than death rate  population grows
 Birth rate equals death rate  population stays the same
 Death rate greater than birthrate  population shrinks
Factors that change population
size:
1.immigration – movement of individuals into a population from
another population
2. births – causes an increase in population size
3. emigration – movement of individuals out of a population and
into another population
4. deaths – causes a decrease in population size
BIRTH
IMMIGRATION
DEATH
EMIGRATION
Under ideal conditions with unlimited resources, a
population will grow exponentially.
• Exponential growth = as a population gets larger, it
grows faster
“J” curve
EXPONENTIAL GROWTH CURVE
Population growth is NOT
limited
 Takes on an J-shape
 Ideal and doesn’t
normally occur in most
populations
 What kinds of organisms
might have exponential
growth and why?

Limiting factor = Any biotic or abiotic factor that
restricts the numbers of organisms
Examples: food, water, shelter, etc
Two types of Limiting Factors:
1. density-dependent
2. density-independent
Density-dependent limiting factors
- affected by the number of individuals in a given area
• competition and availability of food, water and space
• predation
• parasitism and disease
Density-independent limiting factors
- limit a population’s growth regardless of the density
of the population
1. unusual weather
2. natural disasters
3. human activities (pollution or dam building)
CARRYING CAPACITY
 The
maximum number of
individuals that can be
supported by the ecosystem.
 The
limit is determined by the
availability of resources and by
their interactions with other
organisms.
LOGISTIC GROWTH CURVE:
Occurs when population growth is limited by factors
in the environment
Take on the “S” curve
carrying
capacity
• As resources become less
available, the growth of the
population slows or stops.
• Reaches carrying capacity
J-CURVE VS. S - CURVE
All populations will eventually display an
S-curve.

Human Population Growth!
P. 98
REPRODUCTIVE PATTERNS
 Species
of organisms vary in
the number of births per
reproductive cycle, in the age
that reproduction begins, and
in the life span of the organism.
○ R-strategist
○ K-strategist
P. 98
R-strategist
Small organism (fruit fly or a mouse)
 Short life span
 Produce many offspring
 Strategy is to produce as many offspring
as possible in a short time in order to
take advantage of some environmental
factors
 Populations are controlled by densityindependent factors (changes in abiotic
factors)

P. 99
K-strategist (also called Carrying Capacity Strategy)
Large organism (elephant)
 Long life span
 Produce fewer offspring but invest a lot of
care
 Strategy is to produce only a few offspring
who have a better chance of living due the
care they get from parents
 Populations are controlled by densitydependent (biotic factors)

Which are you?
R-strategist
K-strategist
How do humans affect the
populations of species?

Humans have played a large role in the
loss of Biodiversity on the planet.

Biodiversity = the variety of life in an
area
Bio NOTES: Human Impact on the Environment
1. Effects of Human Overpopulation:
• loss of land/habitat
• species extinction
• water and food shortage
• poverty
• poor sanitation
• emerging disease
2. Deforestation – loss of forests
- cause soil erosion, loss of habitat, and species extinction
Worldwide, about half of the area covered by forests has been cleared.
3. Threats to biodiversity – the variety of organisms is decreasing
- an imbalance can cause extinction
4. Pesticide use – using chemicals to kill and control pests
- will sometimes kill non-target species
- pollutes water sources
- causes health problems
5. Biological magnification
– concentrations of a harmful substance increase
in organisms at higher trophic levels in a food web
Effects on Air Quality
Global Warming
• The earth’s atmosphere
keeps some heat from
going out into space
• Pollution in our atmosphere
causes too much heat to
stay on earth
• Changes overall temperature/
climate
• Raises sea level
• Affects health of ecosystems
Acid Rain
Rain that has been made acidic
by certain pollutants in the air.
• pollutants = sulfur dioxide
and nitrogen oxides from
burning fossil fuels
• causes health problems
• damages forests and lakes
• damages buildings
•Harmful to animals
The Greenhouse Effect:
Effects on Water Quality
The runoff of silt, soil, pesticides, and fertilizers from agricultural
land is the largest single source of water pollution.
Eutrophication:
- excess fertilizers can run off into lakes and ponds
- this stimulates plant and algae overgrowth
- a buildup of algae can lower the levels of dissolved oxygen in
the water
- this leads to the dying off of the fish population
- over time, lakes and ponds slowly begin to fill in
Why can’t you just clean up
polluted water?
- it is expensive
- who pays for it?
- technology not available for all types
Effects on Natural Resources
Renewable resources
- can regenerate if they are living or can be replenished
by biochemical cycles if they are nonliving
- ex. trees, fresh water
Nonrenewable resources
- cannot be replenished by natural processes
- ex. fossil fuels
Sustainability = a way of using natural resources without
depleting them for future generations
• use renewable resources that can be “restocked”
• recycle and reuse products
• plant tree farms
• only cut down selected trees instead of clear-cutting
• follow emission standards
The Story of Easter Island
• Humans first landed on Easter Island between 400 and 700 A.D.
• Island had thick forests, rich soil, many bird and animal species
• Human population grew quickly over next 1000 years
• They cut down forests for lumber and boats faster than the trees
could grow back
• Eventually, there were no trees left….no wood for shelter or boats,
rich soil washed away, habitat lost for animal species, no fishing
without boats
• With no food, and island resources nearly gone, the Easter Island
human population crashed and the Easter Islanders disappeared.