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Man’s Impact
The following are some of man’s activities
that can affect a habitat by starting a
negative chain reaction within the food
webs.
 1. Land development
 2. Farming
 3. Pollution
 4. Introducing invader species
 5. Poaching
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Development
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As we build to improve our life, wetland, prairie,
and forest habitats are destroyed and animals
are displaced.
These animals move into the surrounding
habitat causing the different populations to
increase.
This increase in population will cause more
competition for food.
If the carrying capacity of the habitat is
exceeded, some of the animals will starve and
die.
Plants can’t move so they will die.
Nature can impact a habitat too
Floods and fires cause the same type of
chain reaction as development.
 Drought causes the same chain reaction
as the low levels of dissolved oxygen after
an algae bloom.
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When a dam is built across a river to make
a lake, it will cause the same type of chain
reaction as other development because
the habitat will be under water.
 Channelization is when a curving
(meandering) river is made to flow in a
straight line. This speeds up the flow of
the water. It will also make the water
muddier. This causes the same type chain
reaction as development because it
changes the animals habitat.
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Farming Practices
We spray herbicides to kill unwanted plants.
 We spray pesticides to kill unwanted insects.
 We put fertilizer on plants to make them grow
faster and bigger.
 All three of these practices are done to get
larger yields from the crops we grow. This is a
good thing . The problem occurs when we use
too much.
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Herbicides
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Herbicides can enter a wetland, pond or river
after heavy rains. (runoff)
1. The first thing that happens is some of the
plants will die.
2. This will cause an increase in the competition
for food between any of the animals that eat
these plants.
3. Some of the animals that eat plants may
starve and die because there is less food.
4. Fewer first level consumers will effect the
next level consumers and so on.
Pesticides
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Pesticides can enter a wetland, pond or river
after heavy rains. (runoff)
1. The first thing that happens is some of the
insects will die.
2. This will cause an increase in the competition
for food between any of the animals that eat
these insects.
3. Some of the animals that eat insects may
starve and die because there is less food.
4. Fewer second level consumers will effect the
next level consumers and so on.
Fertilizer
Fertilizer can enter a wetland, pond or river after heavy
rains. (runoff)
 1. The first thing that happens is an increase in plant
growth called an algae bloom.
 2. When the extra food from the fertilizer runoff is used up,
some of the surplus plants will die.
 3. As the decomposers (bacteria) break down these dead
plants they will use up the dissolved oxygen in the water.
 4. The lower levels of oxygen will cause some of the fish to
die.
 5. This will cause an increase in the competition for food
between any of the animals that eat these fish.
 6. Some of the animals that eat fish may starve and die
because there is less food.
 7. Fewer second level consumers will effect the next level
consumers and so on.
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More Farming Practices
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Overgrazing is when livestock eats to much of the
vegetation in an area. Overgrazing of a prairie can cause
the same chain reaction as development.
Feedlots contain a large number of animals in a small
area. These animals create a large amount of waste. If
this waste runs off into a wetland, pond or river it can
cause a chain reaction just like fertilizer runoff.
Planting fescue (a type of grass) in a prairie changes the
diversity of the habitat from hundreds of different types
of plants to a single type of plant. This will cause a chain
reaction similar to development.
More problems caused by man
Sewage (human waste) from septic tanks
or waste water treatment plants can have
the same affect on wetlands, ponds and
rivers as fertilizer runoff .
 Oil kills some plants and animals and
makes it hard for others to stay in the
habitat.
 Chlorine is used to kill microscopic plants
and animals in the water.
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Invader Species
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Invader species are not native to Missouri
habitats.
1. They compete with the native species for
food and space.
2. If this new species is more successful, the
native population of plants or animals may
decrease. Causing a chain reaction in the food
webs of a habitat.
Examples:
Zebra mussels compete with native mussels in
a river or lake.
Crayfish compete with the native crayfish.
Asian carp compete with the native fish.
Invader Species continued
Gypsy moth larvae will eat the leaves of a
tree. This will cause the tree to make more
leaves instead of seeds. It also causes the tree
to use up some of its winter reserves which will
stress the tree and possibly cause it to die.
 Purple loosestrife competes with the native
plants in a wetland.
 Musk thistle competes with native plants in a
prairie.
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Illegal Hunting
Poachers taking any animal in large
numbers will have a negative effect on the
food webs of a habitat.
 Lead shot in ducks can have an impact on
the birds of prey in a food web. Lead is
toxic.
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DDT in a food chain
For many years, the chemical DDT was used to kill certain insects that carry
human diseases and attack crops. Then scientists found that DDT harmed
other organisms in food chains. The figure above shows how DDT became
more concentrated in animals’ bodies as it moved through a food chain.
Birds and fish with high levels of DDT could not reproduce successfully, and
their populations decreased. In 1972, the government banned the use of
DDT.
 Why does DDT become more concentrated as it passes up a food chain?
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