Kean University Continuing Education
Implementing the Science Standards K-4
Pyramid of Energy in Ecology
We can consider a typical food chain in the environment. It can be written
In this food chain each component has a definite function.
- Original Source of Energy. The Sun provides the energy that
is used by the Green Plants. The Sun is the original source of energy in
all food chains on the surface of the Earth and in the upper parts of the
- Primary Producer. The green plants are the Primary Producers
for the food chain. The energy from the Sun is converted by the plants
- Primary Consumers. The Insects are the Primary Consumers. They
are the first animals to eat the plants. When they eat the plants and obtain
some of the energy they stored when making food. The rest of the energy
is lost and dissipated as heat.
- Secondary Consumers. Insects are eaten by Frogs. The Frogs are
the secondary consumers in this food chain. They obtain part of the energy
stored by the insects. The remaining energy stored by the insects is lost.
- Tertiary Consumers. Snakes eat Frogs. In this example, the Snakes
are the Tertiary Consumers. They obtain part of the energy that is stored
by the frogs. The rest of the energy is lost.
- Higher Order Consumers. Sometimes there are levels of consumption
above the level of Tertiary Consumers. In many parts of North America,
the top of the food chain is a predatory bird, such as the Eagle.
The Pyramid of Energy in Ecology
The food chain described above can be represented using a pyramid.
The four levels of the pyramid are the Primary Producers, the Primary
Consumers, the Secondary Consumers and the Tertiary Consumers. Notice that
each level is smaller than it would be in a normal pyramid. This indicates
that the population size gets smaller as you go up the pyramid.
- Primary Producers. The green plants depend on sun and water.
If the growing season is very dry, the size of their level in the pyramid
will be smaller. A smaller number of grass plants supports a smaller population
of insects. On the other hand, if there is abundant rainfall and a good
growing season, there will be a larger population of grass plants. A larger
population of grass plants will support a larger population of insects.
These effects are transmitted up the pyramid.
- Primary Consumers. The insect population will depend on the
green plants for food. Since an insect requires more than one plant in
its lifetime, the size of their level in the pyramid is smaller. A smaller
number of green plants will result in a smaller insect population. This
will affect the frog and snake populations.
- Secondary Consumers. The size of the frog population will depend
on the size of the insect population. Since a frog requires numerous insects
to keep alive, the size of the frog population level in the pyramid will
always be smaller than the insect level below it. The size of the frog
population will increase as the insect level increases. However, the frog
population will decrease if the insect level decreases.
- Tertiary Consumers. The snakes depend on the frogs for food.
Since a snake requires numerous frogs in its lifetime, the pupulation of
snakes is always smaller than the frog population. The snake population
expands and contracts in conjunction with the expansion or contraction
of the other levels of the pyramid.
Concentration and Transmission of Environmental Toxins via the Food
Many toxins in the environment are concentrated in the food pyramid
and transmitted upwards through the food pyramid. This is due to the fact
that these toxins are not biodegradable. A biodegradable chemical substance
can be broken down by the metabolic action of bacteria and fungi in the
soil and water. Toxins are not biodegradable so they maintain the poisonous
effects as they are being passed through the food chain.
An exercise to do with students is to estimate how much toxin a snake
will have in its body if each plant has one unit of toxin and the toxins
are amplified 100 times in each level.
- Primary Producer Level. Assume that each grass plant contains
1 unit of a certain toxin.
- Primary Consumer Level. Assume that each insect eats 100 grass
plants during its lifetime. How many units of toxin are present in each
insect? The answer is that each insect will have 1 x 100 units = 100 units
- Secondary Consumer Level. Assume that each frog eats 100 insect
during its lifetime. How many units of toxin are present in each frog?
The answer that each insect contains 100 units x 100 insects per frog =
10,000 units of toxin per frog.
- Tertiary Consumer Level. Assume that each snake eats 100 frogs.
How many units of toxin will be present in each snake? The anwer is that
each frog has 10,000 units x 100 frogs = 1,000,000 (one million) units
of toxin in each snake.
This concentration and amplification of toxins in the food chain was
responsible for nearly wiping out the American Bald Eagle in the United
States during the last half of the 20th century. Widespread, non-point
source use of the pesticide DDT resulted in concentration and amplification
of DDT in the food chain. DDT in the Eagle prevented their eggs from hatching
properly. The Eagle was saved by environmental laws passed by the Congress
in the 1970s.