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Food Webs: Who Eats Who
If you
spent some time in a forest watching the animals that live there, you would realize
that one of their main activities is finding food. All organisms, including people, need
energy to live. Organisms that must eat to live, like people, are called consumers or
heterotrophs. Organisms that can use the sun's energy to make their own food are
called producers or autotrophs. Plants, some algae, and certain kinds of bacteria are
producers. They directly or indirectly provide the energy for all of the organisms in the
ecosystem. Producers must do their job in order for consumers to eat and live.
All life depends
on energy from the sun. Plants can use this energy, through the process
photosynthesis,
of
to make the sugar they need to live and grow. Animals then eat plants
or eat other animals to get the energy they need.
A food chain shows the energy transfer that occurs as something eats something else.
The first level in a food chain is the producers, which get energy directly from the sun.
The next levels are made up of consumers. Consumers can be divided up into categories
like herbivores and carnivores. Herbivores, also called primary consumers, are
animals that eat only plants. Carnivores are animals that eat only other animals. A
carnivore that eats herbivores is called a secondary consumer. Camivores that eat other
carnivores are called tertiary consumers. An example of an ocean food chain might be:
phytoplankton > fish > seal > killer whale.
Most food chains have only four or five links. This is because only a small part of the
energy at the first level in a food chain is passed to the next level. For example, when a
herbivore eats plants, only a fraction of the energy it gets from the plants is passed on to
the carnivore at the next level. This is because much of that energy is lost as waste or
used up by the herbivore to carry out its life processes. A carnivore will need to eat many
herbivores to have enough energy to live and grow. This is why there are many more
herbivores than carnivores. There is just not enough energy left at the top level of a food
chain to support many carnivores.
A food chain shows the flow of energy in a line from what is eaten to the animal that eats
it. A food chain on paper is actually a lot simpler than nature. A food web where some
organisms feed on more than one level is more correct. For example, omnivores are a
type of animal that eats both plants and animals. A grizzly bear is a good example.
Grizzly bears eat plant roots that they dig up, but they also eat animals like fish. There
are also decomposers like bacteria that feed on decaying matter at any level.
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f,'ood Webs: Who Eats Who (contrd)
When humans have tried to change food webs, they have often caused big problems.
Figuring out *who eats who" can be very tricky. In the 1950's in Bomeo, offi"iulr used a
chemical called DDT to kill mosquitoes that were causing disease. This had unexpected
results. In addition to mosquitoes, the wasps, caterpillars, cockroaches, lizards, and cats
that lived there were affected. Once cats started dying, rats carrying fleas that had a
disease called plague moved in which could have made everyone very sick. Oflicials
then had to parachute healthy cats in to get the rats under control! We learned from this
that food webs are more complicated than they may seem at first glance!
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Food \ilebs: Who Eats Who Questions
1.
Consumers must eat to live while
2.
What types of organisms are producers?
3.
Where do producers get their energy from?
4.
What is another word for primary consumers?
5.
What type of food would a secondary consumer eat?
6.
In the example provided, what kind of a consumer is the seal?
7.
True or False. Some energy is lost with each step up a food chain.
8.
A food chain is like
9.
What is an omnivore?
10.
What is a decomposers role in an ecosystem?
make their own food.
food
a line, but a
that shows how some
organisms feed on more than one level is more realistic.
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