Ecology: Energy Transferred in Ecosystems

Ecosystems consist of all the organisms living in a particular area, as well as the abiotic (non-living) components with which the organisms interact.
Producers like _green plants_ provide the original energy source for ecosystems, as they can photosynthesise to convert sunlight energy into chemical energy.
This energy is then _transferred__ through the ecosystem in food chains and webs.
The step-by-step transfer of energy from one organism to another via feeding is described by a food chain.
When multiple food chains intertwine due to organisms feeding at multiple trophic levels, it forms a food web.
Energy is transferred between trophic levels (levels in the food chain) when one organism consumes another.
At every step in a food chain, most of the energy is lost to the surroundings as heat, which is why food chains rarely extend beyond four or five trophic levels.
Primary consumers eat the plants, secondary consumers eat the primary consumers, and so on.

The efficiency of energy transfer between trophic levels can be calculated using the formula: (energy transferred to the next level / total energy intake) x 100.
Typically, only about 10% of the energy taken in at each trophic level is passed on to the next.
The rest of the energy is lost in waste products, respiration (as heat), or is used for growth and other life processes.
This inefficient energy transfer is why there are usually few high-level predators in an ecosystem, as there is not enough energy to support large populations at the top of food chains.
In addition, reductions in primary producer populations (e.g., through deforestation) can have knock-on effects further up the food chain, causing population decreases at higher trophic levels.
Due to inefficient energy transfer and other losses along the food chain, the biomass (total mass of all organisms) decreases from one trophic level to the next.

Pyramids of energy are graphical models representing the quantity of energy at each trophic level of a food chain, with the producers at the base and the top predators at the peak.
Units of measurement are typically energy per unit area per unit time, such as kJ m-2 yr-1.
Unlike pyramids of numbers or biomass, pyramids of energy are always upright (larger at the base), as energy is always lost from one trophic level to the next.
These pyramids show that to support a small number of high-level predators, a large amount of energy needs to be produced at the base of the food chain.
Studying pyramids of energy can illustrate the impact of human activities on ecosystems, e.g., overfishing can lead to an energy imbalance.