The organisms within food chains can be divided into different categories,
producers, consumers and scavengers. They can also be classified by their
trophic level or position on the food chain. Any organism that feeds on a
plant is called a first order consumer or heterotroph. Producers are also
known as autotrophs because they are found on the bottom level of a food
chain.
Plants, or producers, take the energy from sunlight and use it to carry out
photosynthesis - change carbon dioxide into glucose or other sugars. These
sugars contain carbon carbon bonds. As consumers eat producers they break
these bonds which release pure energy for further use.
Light energy --> chlorophyll --> photosynthesis --> glucose --> converted into other carbohydrates (eg glucose, sugars) --> eaten by consumers which use the energy.
Algae is a producer which also uses photosynthesis,. Cyanobacteria or the
dreaded "blue green algae" effects many rivers by clogging waterways as the
plants reproduce rapidly. Bacteria is another common autotroph (producer),
taking energy from a wide variety of sources to form sugars. Bacteria can
be found around deep-sea vents, using the energy from the chemicals coming
out of the earth's interior to create sugars. Bacteria also live deep
underground and use similar sources to convert carbon dioxide into energy.
Consumers eat producers or other lower order consumers. For example, an
organism which feeds on a first order consumer is called a second order
consumer. A decomposer breaks down any dead organisms with the most common
being fungi and bacteria. They convert animal and plant matter back into
nutrients.
An example of these levels in a food chain is:
Sun --> producer (plant) --> first order consumer (herbivore) --> second order consumer (carnivore) --> third order consumer (carnivore) --> bacteria (decomposer).
When these categories are applied to the wallaby food chain:
Grass is eaten by a wallaby is eaten by a dingo is decomposed by bacteria.
The first order consumer is the Wallaby as it eats plant matter. The second
order consumer is the Dingo because it eats the wallaby. The decomposer,
bacteria, breaks down any dead organisms.
Another method of describing a consumers' role in the food chain is to
group them according to the source of their food. Animals which eat plants
are called herbivores, those which eat other animals carnivores and those
which eat both plants and animals omnivores.
Herbivores feed on a primary trophic level so they are also known as
autotrophs and producers. Carnivores feed on the secondary or higher
trophic level and are therefore heterotrophs or a higher order consumer.
Omnivores feed on all trophic levels.
