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Trophic level

The trophic level is the position that an organism occupies in a food chain.

Trophic levels and ecosystems

Ecosystems have four basic components:
  • The abiotic environment
  • Producers
  • Consumers
  • Decomposers

Producers[?] utilise energy form the sun and nutrients from the abiotic environment (carbon dioxide from the atmosphere or water, other nutrients from the soil or water) to develop by means of photosynthesis. Exemples of producers are green plants and phytoplankton. Since they get their carbon from carbon dioxide rather than from organic carbon, they are called autotrophic organisms.

Consumers[?] feed on protoplasm produced from photosynthesis or on other organisms from higher levels. Consumers depends on producers for their energy and synthesis needs. For example, herbivores are primary consumers (and secondary producers). A carnivore that eats only herbivores is a secondary consumer and a tertiary producer.

Decomposers[?] utilise energy from wastes or dead organisms, and so complete the cycle by returning nutrients to the soil or water, and carbon dioxide to the air and water.

Trophic levels and energy

Primary production is generation of biomass through photosynthesis. The highest producers of biomass are
  • tropical rain forests[?], 2000 g/m2/yr of biomass
  • swamps[?] and marshes, 2500 g/m2/yr of biomass
  • algal beds and reefs, 2000 g/m2/yr of biomass
  • estuaries, 1800 g/m2/yr of biomass

Others include

  • Temperate forests, 1200 g/m2/yr of biomass
  • Cultivated lands; 600 g/m2/yr of biomass

while lowest producers are deserts and frozen areas (less than 200 g/m2/yr of biomass).

In the ocean, phytoplankton is the primary producer[?] (the first level in the food chain or the first trophic level).Phytoplankton converts inorganic carbon into protoplasm.
Phytoplankton is consumed by microscopic animals called zooplankton (these are the second level in the food chain).
Zooplankton is consumed by Crustaceans[?] (the third level in the food chain).
Fish eating crustaceans and seals consuming the fishes could constitute the fourth and the fifth trophic level.
Trophic levels are very similar on land, with plants being the first trophic level, cows eating the grass being the second, and humans eating the cows being the third.

The amount of biomass produced for a given amount of solar energy is highest at the first level. Less biomass is produced at the second level, for some energy is lost during the conversion. The more trophic levels there are, the more energy is lost through conversion.

Humans are generally primary and secondary consumers, and thus represent usually second and third trophic levels. Most humans are omnivores[?], which means they consume both plants and animals. Less energy is required to support vegetarian human than omnivores ones, for there is a significant energy loss during the conversion of grain and vegetables in animal matter.

Trophic levels and biodiversity

Each species in an ecosystem is affected by the other species in that ecosystem. There are very few single prey-single predator relationship. Most preys are consumed by more than one predator, and most predators have more than one prey. Their relationships are also influenced by other environmental factors.
biodiversity (seen along the specific diversity point of view) gives ecosystems stability. When consumers have several differents producers available for food, the disappearance of one is not likely to have a lot of impact. However, for a consumer which has only one or a few producer, a decrease in the producer population is likely to affected it strongly.

Reduction of habitat, hunting and fishing of some species to extinction or near extinction, eradication of insects and pollution, tend to tip the balance of biodiversity. Similarly, in-situ conservation areas need to be carefully designed to maintain a diverse and stable environnement for the extinct species to thrive.

See also



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