Ecosystem Energy Flow Notes

Energy Movement Through Ecosystems

Every activity organisms undertake requires energy. The flow of energy dictates the kinds and amount of organisms that can survive in an ecosystem.

Photosynthetic organisms form the base of most life on Earth.
They convert sunlight into chemical energy stored in organic molecules.
These organic molecules are considered food.
Primary productivity is the rate at which photosynthetic organisms produce organic material (food) in an ecosystem.
Producers (bacteria, plants, algae) initially capture energy through photosynthesis.
Consumers acquire energy by consuming plants or other organisms.

The first and lowest level consists of producers such as algae, bacteria, and plants.
Producers create energy-rich carbohydrates using solar energy.
They also absorb nitrogen gas and other substances from the environment.

The second level consists of herbivores like cows, horses, caterpillars, and some ducks.
Herbivores consume plants or other primary producers.
They rely on microorganisms (bacteria and protists) in their guts to digest cellulose from plants.
Humans lack these microorganisms and cannot digest cellulose.

Secondary consumers, which are animals that eat other animals, occupy the third level.
Examples of carnivores at this level include tigers, snakes, and wolves.
Omnivores (bears and humans) also belong to this level because they consume both plants and animals.
Since humans cannot digest cellulose, they consume simple sugars and starches from plants.

Detritivores, including bacterial and fungal decomposers and worms, exist in every ecosystem.
They obtain energy from dead bodies and organic wastes from all trophic levels.
Bacteria and fungi function as decomposers, causing decay.
Decomposition releases nutrients back into the environment for other organisms to use.

Most ecosystems have a fourth trophic level with tertiary consumers (top carnivores).
Eagles, which eat snakes, are an example of tertiary consumers.

Ecosystems rarely have more than four trophic levels due to energy loss.
Energy transfer is not always linear; some organisms feed at multiple trophic levels, creating a food web.

As organisms feed to gain energy, potential energy in chemical bonds is released and used.
Some energy converts to other forms of potential energy, some aids cellular processes, but much is dispersed as heat into the environment.

As energy moves up trophic levels, useful energy decreases as much of it disperses as heat.
This is why ecosystems rarely exceed four trophic levels.
Organisms acquire only about 10% of the energy from the previous trophic level.

Too much energy is lost between trophic levels to support more than three or four levels in most ecosystems.
A large human population could not survive by only eating lions from the Serengeti due to insufficient lion numbers.
The grass needed to support zebras, which in turn support lions that would feed humans, would be impossible to obtain.
Adding a trophic level increases the energy demand on consumers by a factor of about 10.
The number of individuals in a trophic level does not accurately indicate the amount of energy in that level.
Larger organisms consume more energy.
Measuring biomass is a more accurate method for determining energy availability in trophic levels.
Biomass is the weight of organic matter in an area.
Each higher level in the energy pyramid contains only about 10% of the biomass from the level below it.