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Humans and
the
Environment
Threats to
Biodiversity
Biodiversity
refers to the variety of species in a
specific area.
Most biologists are confident that there are at least 10
million species on Earth— and as many as 30 million.
After about 200 years of cataloging, scientists have
named and described fewer than 3 million species.
• The simplest and most common measure of
biodiversity is the number of different species
that live in a certain area (pg 111)
• Tropical regions contain two-thirds of all land
species on Earth. The richest places for
biodiversity seems to be warm places:
Places of great
biodiversity
Tropical rainforest
Coral reef
and large tropical lakes.
Biodiversity is important.
1) Living things are interdependent.
Animals could not exist without green plants.
Many flowering plants could not exist without
animals to pollinate them.
Plants are dependent on decomposers that break
down dead or decaying materials into nutrients
they can absorb.
In a rain forest, a tree grows from nutrients
released by decomposers. A sloth eats
leaves of the tree. Moss grows on the
back of a sloth. Thus living things can be
niches for other living things.
Populations are adapted to live together in
communities. Although ecologists have
studied many complex relationships
among organisms, many relationships are
yet to be discovered.
2) Scientists do know that if a species is lost
from an ecosystem, the loss may have
consequences for other living things in the area.
An organism suffers when a plant or
animal it feeds upon is removed
permanently from a food chain or food
web. A population may soon exceed the
area’s carrying capacity if its predators
are removed.
If the symbiotic relationships among
organisms are broken due to the loss of
one species, then the remaining species
will also be affected.
3) Biodiversity can bring stability to an
ecosystem. A pest could easily destroy all
the corn in a farmer’s field, but it would be
far more difficult for a single type of insect
or disease to destroy all individuals of a
plant species in a rain forest.
4) Humans depend on other organisms
for their needs. Oxygen is supplied &
carbon dioxide is removed from the air by
diverse species of plants and algae living
in a variety of ecosystems throughout the
world.
5) Think of all the food products that
people eat, yet only a few plant and
animal species supply the major
portion of food eaten by the human
population. Biodiversity could
help breeders produce additional
food crops.
• 6) Biodiversity can be used to help
improve people’s health.
• Living things supply the world pharmacies.
Active chemical compounds in many
manufactured drugs are usually first
isolated in living things.
The Extinct and the Endangered.
Species can become extinct if every last member
disappears. It is a natural process --- natural
background extinction occurs at a rate of about one
species per year per one million species. However, the
current rate is many times that. Scientists hypothesize
that this may be due to needs of the expanding human
population, habitat loss, and land exploitation.
A species is considered endangered
when its numbers become so low that
extinction is possible. (Pg 115) When a
population of a species is likely to become
endangered, it is said to be a threatened
species.
Threats to Biodiversity:
Habitat loss - rain forests cleared to create
farmland and supply firewood. Much of
the land soon becomes useless for farmland
due to the lack of nutrients.
Habitat fragmentation is separation of
the wilderness areas from other
wilderness areas ----usually due to
development of the land for human
population. It increases extinction of
local species, disrupts ecological
processes, changes local climate, and
contributes to the species migration.
Habitats can become too small for finding
food and mates.
Damage to habitats by pollution:
Air, water and land pollution
Acid precipitation is linked to deterioration
of forests and lakes. Sulfur dioxide from coalburning factories and nitrogen oxides from
car exhaust combine with water vapor in the
air to form acidic droplets.
This moisture leaches calcium, potassium,
and other nutrients from the soil. It has
been linked to degrading lake
ecosystems.
• Ozone layer depletion – less ozone in
the atmosphere means that less UV
radiation is blocked causing damage to
living organisms. (pg 118)
• (CFCs – Chlorofluorocarbons – the
enemy of ozone)
Global warming: Excess, manmade CO2 pollution has
been seen as contributing to global warming. CO2 is a
greenhouse gas that traps heat from escaping the Earth.
Burning fossil fuels adds a great deal of CO2 which
scientists claim will raise global temperature and cause
climate changes. This may have a disastrous effect on
the populations of many organisms around the
world.
Water pollution
A variety of pollutants can affect aquatic life.
Excess fertilizers and animal wastes are often
carried by rain into streams and lakes. These
nutrients causes the excessive growth of algae
(algal blooms). The algae dies, sinks, decays, &
removes O2 from the water. Silt from eroded soil
can enter the water and clog fish gills.
Detergents, heavy metals and industrial
chemicals can cause death of aquatic
organisms.
Land pollution Trash, solid wastes-cans, paper, plastics,
metals, dirt and spoiled food are thrown away every day. The
average American produces about 1.8 kg of solid waste daily.
Billions of tons of solid waste are buried in landfills. Strict
controls on the design, construction and placement of landfills
are meant to reduce groundwater contamination.
Pesticides and other
chemicals can lead to habitat
degradation. DDT, a chemical
used to control mosquitoes,
found its way into the food chain
in birds, insects, fish and other
small animals. The DDT was
passes on to animals that
preyed upon these affected
animals.
Bald eagles and peregrine falcons were found to
lay eggs with shells that cracked easily, killing
the chicks. This caused a sharp decline in their
populations. DDT has been banned since 1972
in the U.S..
Invasion species or exotic species are those accidently
introduced into an ecosystem. They can be a problem for
native species. After the Erie canal was built, the sea
lamprey found its way to the Great Lakes and totally
eliminated certain fish species from some of the Great
Lakes.