Trophic Pyramid | Definition & Examples - Britannica

Home » What Does An Energy Pyramid Show » Trophic Pyramid | Definition & Examples - Britannica

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The base of the pyramid

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The organisms that make up the base level of the pyramid vary from community to community. In terrestrial communities, multicellular plants generally form the base of the pyramid, whereas in freshwater lakes a combination of multicellular plants and single-celled algae constitute the first trophic level. The trophic structure of the ocean is built on plankton, specifically phytoplankton (flora that use carbon dioxide, release oxygen, and convert minerals to a form animals can use). Zooplankton, such as krill, also play important roles, both as consumers of phytoplankton and as food for a wide variety of marine animals. There are some exceptions to this general plan. Many freshwater streams have detritus rather than living plants as their energy base. Detritus is composed of leaves and other plant parts that fall into the water from surrounding terrestrial communities. It is broken down by microorganisms, and the microorganism-rich detritus is eaten by aquatic invertebrates, which are in turn eaten by vertebrates.

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trophic pyramid
trophic pyramidTrophic pyramid, also called an energy pyramid, showing the progression of food energy. The pyramid base contains producers, organisms that make their own food from inorganic substances. All other organisms in the pyramid are consumers. The consumers at each level feed on organisms from the level below and are themselves consumed by organisms at the level above. Most of the food energy that enters a trophic level is "lost" as heat when it is used by organisms to power the normal activities of life. Thus, the higher the trophic level on the pyramid, the lower the amount of available energy.(more)

The most unusual biological communities of all are those surrounding hydrothermal vents on the ocean floor. These vents result from volcanic activity and the movement of continental plates, which create cracks in the seafloor. Water seeps into the cracks, is heated by magma within Earth’s mantle, becomes laden with hydrogen sulfide, and then rises back to the ocean floor. Sulfur-oxidizing bacteria (chemoautotrophs) thrive in the warm, sulfur-rich water surrounding these cracks. The bacteria use reduced sulfur as an energy source for the fixation of carbon dioxide. Unlike all other known biological communities on Earth, the energy that forms the base of these deep-sea communities comes from chemosynthesis rather than from photosynthesis; the ecosystem is thus supported by geothermal energy rather than solar energy.

Some species surrounding these vents feed on these bacteria, but other species have formed long-term, reciprocally beneficial relationships (mutualistic symbioses) with sulfur bacteria. These species harbour the chemoautotrophic bacteria within their bodies and derive nutrition directly from them. The biological communities surrounding these vents are so different from those in the rest of the ocean that since the 1980s, when biological research of these vents began, about 200 new species have been described, and there are many more that remain undescribed—i.e., not formally described and given scientific names. Among the described species there are at least 75 new genera, 15 new families, one new order, one new class, and even one new phylum.

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