 A group of individuals of the same species in a given area
Population Density – the number of individuals of
a species in a given area
Under ideal conditions , the
population density of living
things can increase explosively
-Elephant seals – hunted nearly to
extinction (20 individuals) 1890
Population in 1991
127,000 and growing
exponential growth
 Elephant Seals –
were hunted to near extinction (8 - 20 individuals) in
1890
Hunting was outlawed
Numbers began to increase
127,000 seals by 1991
 Populations can’t continue to grow indefinitely –
 Limiting Factors - Limit the number of organisms in
an ecosystem
- productivity of ecosystem (food supply)
- predators - seasonal changes in the ecosystem
- disease
- cover - water
 Carrying Capacity - the greatest number of individuals
in a population that an ecosystem can support at a
given time
-when a population exceeds carrying capacity it will
decline
During times of population increase, birthrate exceeds death rate
During times when population declines death rate exceeds birth rate
 When a population density greatly exceeds carrying
capacity, the ecosystem is damaged
- leads to a crash in population density
- carrying capacity of the ecosystem is permanently
reduced
 Two activities caused significant changes in carbon cycle:
 Burning Fossil Fuels – releases large amounts of CO2
 Converting forests to agricultural land – reduces the amount
of CO2 that is removed from the atmosphere
 Excess CO2 traps heat
raising average global
temperature - Global
climate change
 Concerns
 Melting glaciers and rising sea Levels
 Water shortages
 Warmer ocean surface temperatures = more intense
hurricanes
 Pestilence – insects and disease
 Habitat loss – coral reefs, alpine meadows, tundra
 Species loss – polar bear (food), green sea turtle (nest),
North Atlantic right whale (food), giant panda (food),
orangutan (fire), elephants (drought), frogs
(reproduction), and tigers (habitat)
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rocks
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Plants and animals
require phosphorus
to make nucleic acids
- it is locked in
rocks
- natural erosion
releases phosphorus
- humans mine it and
use as a fertilizer
finds its way into
lakes etc…..
 Use of Nitrogen and Phosphorus as fertilizers –
-produces large quantities of food (good)
- excess fertilizer runs into lakes, streams etc… (bad)
- algae blooms and then dies.
- dead algae decompose using up the oxygen
in the water
 Acid rain – Sulfur emissions from burning fossil fuels
fall as acid rain – kills forests and aquatic life
 Ozone (O3) depletion – Ozone layer which protects us
from UV radiation is being damaged by CFC’s =
greater risk of cancers
 Smog – air pollutants – damage lungs shortens life
 The following is from a 1968 report on the Cuyahoga River
The surface is covered with the brown oily film observed upstream as far as the Southerly
Plant effluent. In addition, large quantities of black heavy oil floating in slicks, sometimes
several inches thick, are observed frequently. Debris and trash are commonly caught up in
these slicks forming an unsightly floating mess. Anaerobic action is common as the
dissolved oxygen is seldom above a fraction of a part per million. The discharge of cooling
water increases the temperature by 10 to 15°F. The velocity is negligible, and sludge
accumulates on the bottom. Animal life does not exist. Only the algae Oscillatoria grows
along the piers above the water line. The color changes from gray-brown to rusty brown as
the river proceeds downstream. Transparency is less than 0.5 feet in this reach. This entire
reach is grossly polluted.
The river has caught fire at least 13 times the last time was 1969
 Legislation was passed to clean up lakes and streams
- the Clean Water Act – passed in 1972 set standards
for surface water quality
- essentially all navigable surface water must be fit for
human sports and recreation.
- The Environmental Protection Agency was created
Cuyahoga river today
 Soil can take up to 1000 years to form 1 inch
Once topsoil is lost, it is effectively gone for good