Ecosytem Ecology- Energy Flow

Ecosystems include all of the biotic components that we talked about in a community as well as abiotic characteristics. Ecosystem ecologists focus on the flow of energy and nutrients through the ecosystem.

Energy Flow

Energy is required to do the "biological work" needed to keep species alive. Almost all of the energy used by biological organisms on earth originates as electromagnetic energy from the sun that is then converted into chemical energy by the process of photosynthesis. Energy then flows up the food chain from one tropic level to the next.

Secondary Consumers
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Primary Consumers
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Primary Producers

Photosynthetic organism (plants and photosynthetic bacteria) are known as "Primary Producers" and they make up the bottom of most food chains. Species that get their energy by eating primary producers are known as "Primary Consumers". Organims that get their energy by eating primary consumers are known as "Secondary Consumers".
Thus, energy moves up the food chain from primary producers to primary consumers to secondary consumers.

All organisms are releasing energy to the atmosphere in the form of heat (you are releasing heat right now by the effort you are making to keep your eyes open).

When organims die energy is held in their dead bodies. Decomposers "feed" on the energy held in dead bodies and decomposers also release energy to the atmosphere as heat.

3 Key Facts About Energy Flow

1. Energy enters the system as sunlight energy, moves up the food chain, and is ultimately lost as heat.

2. The flow of energy is one way only.

3. The flow of energy from one trophic level to the next is inefficient. Only approximately 10% of the energy held in one trophic level is passed on to the level above it. The

Energy Pyramid

Because the flow of enrgy up the food chain is inefficient, the amount of energy available in each trophic level decreases as you move up the food chain. This can be shown in a diagram known as an "energy pyramid" (see example at the top of the post).

This is important for two reasons. First, there is a limit to how long food chains can be because there is eventually not enough energy available to add another level to the chain. Second, the amount of energy in a trophic level influences the population size of species in the trophic level above it. For example, all else being equal we expect population sizes of predators to be smaller than the population sizes of herbivores because they have less energy to feed on.

Expected Learning Outcomes

At the end of this course a fully engaged student should be able to

- identity the source of most energy used by biological organisms on earth and explain the energy transformations experienced by this energy (TEKS 112.43. 9D,12A, & 12E and TEKS 112.44. 6A, 6B, & 6D)

- diagram the energy pyramid and explain why it has the shape it does and how it affects population structure at different trophic levels (TEKS 112.43. 9D & 12A and TEKS 112.44. 6B, 6C, & 6D).

- diagram food chains and food webs from a variety of environments (TEKS 112.43. 9D, 12A, & 12E and TEKS 112.44. 6B, 6C, & 6D).

- develop curricular materials to illustrate the food web and pattern of energy flow in a chosen environment (TEKS 112.43. 9D, 12A, & 12E and TEKS 112.44. 6B, 6C, & 6D).