Key Concept 1: All energy transferred through food chains and webs is
derived from the Sun.
The source of all energy on Earth is the Sun. However sunlight is not
usable food for animals. It must first be changed to a usable form by
plants. Animals, not able to produce their own food, are required to eat
plants or other animals to gain energy. An example is grass which absorbs
sunlight and is eaten by a grasshopper, which is eaten by a toad, which
gets eaten by a snake, which finally gets eaten by a hawk. In time the
hawk dies, decays, and is broken down by the decomposers which return
the nutrients back to the soil which is used again by nearby plants. A food
chain shows the transfer of this energy.
Sometimes more than one animal will eat a mouse, for example, and a
complex set of energy transfers occur. The interconnected food chains are
called a food web. Regardless of how simple a food chain may be, or
how complicated a food web becomes, the Sun is still the original source
of energy for all living things.
Key Concept 2: Producers use the Sun’s energy to create their own
food through photosynthesis.
Plants use sunlight, water, and carbon dioxide to make glucose, a type of
sugar the plant uses for food. When animals eat plants, the energy stored
in the plant is transferred to the animal. Only plants produce their own
food, so they are called producers. From the smallest green algae in a
pond to the largest tree on earth, all plants produce their own food
through photosynthesis.
Key Concept 3: Consumers and decomposers get their energy from
producers or other consumers.
Some animal consumers get their energy by eating plant producers. Other
animal consumers get their energy by eating other consumers (animals).
Some animals eat both plants and other animals to obtain energy.
(Decomposers such as bacteria and fungi, are organisms that break down
dead organisms and their wastes to get energy.)
Key Concept 4: The different parts of a food web are producers,
consumers, and decomposers.
In order to ensure a successful interactive ecosystem, there must be
a proper balance in the populations of organisms within a food web. Any
change in the population of any organism in the food web or food chain
will affect other organisms. If all the grass in an area was killed in a
wildfire, there would be less grass for the deer to eat and they could die
off. If there were not enough deer to eat, then the predators (coyotes)
would die off. If any population of organisms changes in some way, either
increasing or decreasing, it will affect other organisms in the food web.
Ultimately decomposers, through their chemical breakdown of the
remains of dead plants and animals, return the nutrients in those
decaying bodies back to the soil. This decaying material becomes soil
“humus”, a rich organic material that supports plant growth and the food
web continues.