Energy transfer through an ecosystem - An Overview
Ultimately ALL energy in an ecosystem comes from the Sun. We have learned that plants capture energy from the sun to run a reaction called photosynthesis. Recall that during photosynthesis, the plant produces glucose to store energy for later use. In this way plants "convert" radiant energy from the sun into chemical energy in the form of food (glucose).

The method that organism use to get energy for themselves is called its TROPHIC LEVEL.

TROPHIC LEVELS:
AUTOTROPHS: ("self-feeder") Organisms that can produce their own food. Plants are autotrophs. They produce their own food.

    PRODUCERS: Plants are producers. They capture the energy of light from the sun to make food for themselves through the process of photosynthesis.

      Grass is an example of a producer.

HETEROTROPHS: ("other-feeders") Organisms that depend on others to produce food. Heterotrophs eat other organisms. THERE ARE SEVERAL LEVELS OF HETEROTROPHS.

    PRIMARY CONSUMERS: THE FIRST LEVEL CONSUMERS. When an organism eats plants, they act as a primary consumer. When you eat a salad or a piece of bread, you are acting as a primary consumer. A special group of primary consumers that eat only plants are the HERBIVORES.

    A field mouse is an example of a primary consumer.

    SECONDARY CONSUMERS: THE SECOND LEVEL CONSUMERS. An organism that eats something that ate a plant! When you eat a hamburger, you are acting as a secondary consumer. You have eaten a cow, that ate some grain or grass.

    A snake is an example of a secondary consumer.

    TERTIARY CONSUMERS: THE THIRD LEVEL CONSUMERS. An organism that eats something, that ate something that ate a plant! When you eat a tuna fish sandwich you act as a tertiary consumer. A Tuna eats smaller fish, that eat smaller fish than them, that eat plants and plankton.

    A hawk is an example of a tertiary consumer.

There are three special classes of secondary and tertiary consumers.

    CARNIVORES: organisms that only eat meat. A hawk or a lion are examples of carnivores.

    OMNIVORES: organisms that can and do eat meat, but also eat plants. a human or a bear is an example of an omnivore.

SCAVENGERS: Carnivorous organisms that only eat dead animals.
DECOMPOSERS: Organisms that break down dead organic matter. Fungi, many insects and bacteria are decomposers. They "eat" the dead organic matter to derive energy and materials for growth and development.

They return nutrients to the soil to be used again by plants. If there were no decomposers, the plants would take nutrients out of the soil and it would never be returned. Eventually there would be no more nutrients left, the plants would die. If the plants all died, animals would soon follow!

ECO-PYRAMIDS: The concept of a pyramid is useful to describe the energy (trophic) levels of organisms, the amount of biomass, and amount of energy transferred from one trophic level to another.

    The base of a pyramid is the widest part. Producers are at the base of the eco-pyramid. There are more producers than any type of organism in an ecosystem. 100% of the energy captured from the sun is in the base. There is much more biomass in the base than anywhere else in the pyramid.

    The second level up a pyramid is smaller than the base. Here is where the primary consumers are placed. There are fewer primary consumers than producers. There is only about 10% of the biomass that is found in the base. Only 10% of the energy captured from the sun by the producers is passed up to this level.

    The third level up the pyramid is smaller than the second. Here is where the secondary consumers are placed. There is only about 1% of the biomass that is found in the bass (That's 10% of the biomass in the level below it!). This level has only 1% of the energy that is captured from the sun. (That's 10% of the energy in the level below it!)

    The fourth level is the last level. It is the last level because there is not enough energy left to pass up to another level. This is the level of the tertiary consumer. Only 0.1% of the energy captured by the producers makes it up to this level. Only 0.1% of the biomass in the ecosystem is contained in this level as well.

GENERAL PATTERNS IN THE ECO-PYRAMID:

    "THE 10% RULE"

    - Only 10 % of the energy from a level is passed up to the next level

    - Only 10 % of the biomass from a level is passed up to the next level

There are always fewer individuals in the populations as you go up the pyramid.

The higher you go on the pyramid, the less energy is available!

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