Energy Pyramids

Energy cannot be created or destroyed, but it does change form as it passes from one trophic level to another.

Most energy in ecosystems comes from the sun, captured by autotrophs through photosynthesis.
Herbivores eat the autotrophs and carnivores eat the herbivores.
With each trophic level, some energy is passed on, but most is lost as heat.
Energy Pyramids are diagrams that reflect the amount of available energy at each trophic level.

Energy Flow Through the Ecosystem

Like a river, energy flows in one direction through the living things on earth: Sun --> Autotrophs --> Heterotrophs --> Heat. It does not cycle, like matter, and get back to where it started.

In producers, chlorophyll captures sunlight during photosynthesis.
The energy gets converted from light waves to the chemical bonds of organic molecules like glucose.
Glucose is used by plants and animals to make ATP which is used for all cellular processes from molecular pumps to movement.
Organisms use most of (90%) of their energy for life processes. That energy is eventually converted to heat and given off.
Roughly 10% of the energy an organism take in is available to another organism that consumes it.
The result is much less available energy as it moves up the food chain.

Implications of Energy Pyramids

An energy pyramid shows available energy, usually in some measurement like calories, but available energy also affects characteristics like population size and biomass.

When you look out at any natural setting, the most abundant organisms are probably producers - trees, grass etc.
The most common mammals are probably herbivores - squirrels, rabbits, deer
Carnivores, like foxes or bears, are much more rare because it takes a much larger range to supply them with enough energy to survive.

Humans are omnivores, and our food choices require different amounts of energy.

Plants are the easiest (cheapest) food options
Most of the animals we eat are herbivores, but meat costs more. It takes roughly 10 pounds of chicken feed for every 1 pound of chicken meat. (10% is passed on)
It doesn't make sense to eat carnivores: 100 pounds of feed to raise 10 pounds of herbivores to feed to the carnivore and get 1 pound of meat.
The only real carnivores we eat are fish - that have entire oceans to provide calories, even so, overfishing is a problem.