Primary producers—usually plants and other photosynthesizers—are the gateway for energy to enter food webs.
Productivity is the rate at which energy is added to the bodies of a group of organisms—such as primary producers—in the form of biomass.
Gross productivity is the overall rate of energy capture. Net productivity is lower, adjusted for energy used by organisms in respiration/metabolism.
Energy transfer between trophic levels is inefficient. Only about 10% of the net productivity of one level ends up as net productivity at the next level.
Ecological pyramids are visual representations of energy flow, biomass accumulation, and number of individuals at different trophic levels.
Introduction
Have you ever wondered what would happen if all the plants on Earth disappeared—along with other photosynthesizers, like algae and bacteria?
Well, our beautiful planet would definitely look barren and sad. We would also lose our main source of oxygen, that important stuff we breathe and rely on for metabolism. Carbon dioxide would no longer be cleaned out of the air, and—as it trapped heat—Earth might warm up fast. And, perhaps most problematic, almost every living thing on Earth would eventually run out of food and die.
Why would this be the case? In almost all ecosystems, photosynthesizers are the only "gateway" for energy to flow into food webs—networks of organisms that eat one another. If photosynthesizers were removed, the flow of energy would be cut off, and the other organisms would run out of food. In this way, photosynthesizers lay the foundation for every light-receiving ecosystem.
Producers are the energy gateway
Plants, algae, and photosynthetic bacteria act as producers. Producers are autotrophs, or self-feeding organisms, that make their own organic molecules from carbon dioxide. Photoautotrophs, like plants, use light energy to build sugars out of carbon dioxide. The energy is stored in the chemical bonds of the molecules, which are used as fuel and building material by the plant.
The energy stored in organic molecules can be passed to other organisms in the ecosystem when those organisms eat plants or other organisms that have previously eaten plants. In this way, all the consumers—or heterotrophs, other-feeding organisms—of an ecosystem rely on the ecosystem's producers for energy. Consumers include herbivores, carnivores, and decomposers.
