HUMAN IMPACT ON ECOSYSTEMS
Key Idea : The Earth has finite resources. Increasing human consumption resources places stress on the
natural processes that renew some resources and deplete those resources that cannot be renewed.
Limited Resources – earth has a finite supply of resources
Renewable Resources – natural resources that can be replaced
Ex) sun, water, wind, trees
Nonrenewable (Finite) Resources – cannot be replaced; they exist in limited amounts and take
thousands to millions of years to form
Ex) fossil fuels (coal, oil, natural gas), copper, gold
Key Idea : Humans are part of Earth’s ecosystems. Human activities can, deliberately or inadvertently,
alter the stability of ecosystems. Humans modify ecosystems as a result of population growth, consumption
of natural resources, pollution and technology.
Population Growth – the #1 problem we face on earth; for thousands of years, the human population grew slowly. Then
about 300 years ago, our food supply began to increase, and improvements in health care and hygiene led to dramatic increases in our
population. Now the population is growing at a dangerously fast rate. If the human population continues to grow at this rate, Earth’s
carrying capacity could be reached soon which could be catastrophic. There might not be enough food, water, space, and oxygen for
everyone. The resulting deaths from famine, disease or wars over resources could reduce the human population to a small fraction of
its present level.
Human Activities and the Loss of Diversity
Key Ideas :
 Human destruction of habitats through direct harvesting, pollution, atmospheric changes and other factors
is threatening the stability of the ecosystems that make up Earth’s biosphere.
 Humans influence on other organisms occurs through land use and pollution. Land use decreases the
space and resources available to other species. Pollution changes the chemical composition of the air,
soil and water.
 Humans can alter ecosystems by adding or removing specific organisms – sometimes with serious
consequences. Examples include mono-cropping and imported species.
 Industrialization increases the demands for energy and other resources, including fossil and nuclear fuels.
These energy demands can have positive and negative effects on humans and ecosystems.
Direct Harvesting – destruction or removal of species from their habitats
Ex) slaughtering, poaching, taking animals from wild & putting them in zoos/pet stores
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Land Use – as human populations , our use of land  the space & resources available for other species
Habitat Destruction – as habitats are destroyed, whole ecosystems can be damaged and entire species may
become endangered or even extinct. Ex) rain forest destruction
Deforestation – destruction of forests resulting from human activity
Leads to a lack of biodiversity.
Biodiversity – wide variety of species living together in an ecosystem; increases stability
A loss of biodiversity will lead to an unstable ecosystem and possible losses of medicines.
Invasive (Exotic/Imported/Alien) Species – biodiversity is often reduced when people import and release a
species from environment into another
a) often have no natural enemies in the new ecosystem & rapidly overpopulate the area
b) crowd out, feed on, or otherwise eliminate native species
Ex) purple loosestrife, zebra mussels, snakehead, asian carp
Control of Imported/Invasive Species
1. Direct Removal
a. removal and burning of plant species (ex. purple loosestrife)
b. catch & kill (invasive fish species)
c. trap & kill (Japanese beetle traps)
2. Chemical Control
a. herbicides (kill plants)
b. insecticides (kill insects)
MAY CONTRIBUTE TO WATER, AIR & SOIL POLLUTION.
3. Biological Control – introducing a natural enemy or predator of the invasive species into the
community to control the population of the pest
Advantages :
-lower amounts of toxic chemicals required to kill the pests, which in turn decreases air,
soil, and water pollution
-not harmful to humans
Disadvantage: The newly-introduced species may end up becoming a pest itself
Other ecologically friendly methods of pest control (invasive or not):
 natural insecticides (based on chemicals that plants make to protect themselves from insects)
 physical barriers (putting up fences around home gardens or shrubs)
 insect sterilization (prevents reproduction of pest species)
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Impact of Technology and Industrialization
Nuclear Fuel – 1) power plants cause thermal (heat) pollution of waterways
2) disposal of radioactive nuclear wastes is a problem
Factories also use large amounts of water
Water Pollution – rivers, lakes, and oceans are easy places for people to dispose of wastes, including sewage,
wastes from homes and factories, and animal wastes from farms
Toxic Wastes – poisonous wastes to organisms
ex) chemical fertilizers, pesticides
The level of toxins increases as it moves through the food chain.
- Small quantities of toxic substances are absorbed into the cells of algae and other producers living in the water. When those
producers are eaten by small herbivores, the toxins are stored in the herbivore’s fatty tissue. There it stays until the herbivore
is eaten by the next consumer in the food chain. At each level in the chain, larger and larger amounts of toxic material collect
in the fatty tissue.
Ex) pesticide DDT → plants → small fish → large fish → eagles; eggs were produced with very thin
shells so population declined
Thermal Pollution - power plants heat up water which causes oxygen to decrease
Fertilizer Runoff (artificial eutrophication) – leads to an increase in nitrogen & phosphorus in bodies
of water. This causes algae blooms which will lead to a  in oxygen content of the water
Air Pollution – most of the pollutants released into the atmosphere eventually wind up in the water cycle and
return to the water or land
Burning Fossil Fuels – factories, automobiles & most power plants burn fossil fuels; adds CO2 &
nitrogen and sulfur oxides
Acid Precipitation – caused when nitrogen & sulfur oxides combine with H2O to form nitric &
sulfuric acid; lower pH level, damaging plants & algae as well as microorganisms which disrupts
ecosystems
Smog – sunlight and clouds trap gases into an area creating a polluted haze
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Global Warming – greenhouse gases in the atmosphere trap and absorb infrared radiation that bounces off
Earth’s warm surface. This keeps the earth’s surface warm but in recent years the amount of gases has
increased. The result is the Earth’s average temperature is rising.
Effects: could lead to changes in climate patterns and melting of the ice caps of the poles which could cause
ocean levels to rise and coastal flooding with droughts in other areas
Ozone Depletion – using certain industrial gases has led to the destruction of much of the ozone shield, the
layer of gas in the upper atmosphere that protects Earth from some of the sun’s radiation. This “hole” allows
above normal amounts of ultraviolet radiation from the sun to reach Earth.
Main Cause – release of CFC’s into atmosphere; CFC’s uses as coolants in refrigerators, air conditioners; also
used in aerosols & styrofoams
Main Result – causes hole in ozone shield allowing more UV radiation to reach earth’s surface; ↑ risk of skin
cancer
Key Ideas :
 Societies must decide on proposals that involve the introduction of new technologies. Societies (and
individuals) need to make decisions that assess the risks, costs, benefits and trade-offs associated with
these new technologies and their impact on the environment.
 A trade-off is an exchange of one thing in return for another to achieve a desired result. Ecological
decisions often involve trade-offs  an example might be giving tax breaks to companies that are
involved in alternative energy sources OR taxing companies that produce high levels of CO2 emissions.
What can humans do to protect our ecosystems?
1. Conservation
Example: turn off water when brushing teeth, take shorter showers
2. Restoration
Example: replant seedlings after cutting trees down
3. Reduce, Reuse & Recycle
Examples: paper, glass, plastic, aluminum
4. Research & Technology
Examples: fracking, hybrid vehicles, hydrogen fuel cells, more efficient solar & wind power
5. Environmental Awareness
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