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The Major Types of Ecosystem Organisms

Food chains and food webs describe the flow of energy and nutrients through organisms in an ecosystem. The entry point into the food web are the primary producers, with other organisms feeding on the primary producers or each other. The food web progresses until organisms die or excrete waste, which is broken down by decomposers. While organisms in a food web may be given a specific trophic level, many organisms fulfill multiple roles at various times. For example, omnivorous animals may shift between being a primary consumer feeding on plant material to a secondary or tertiary consumer feeding on other animals as food availability changes.
  1. Primary Producers

    • Primary producers are organisms that uptake nutrients and energy from inorganic sources and convert it into usable energy and nutrients for themselves and consequently, any organisms that feeds on the primary producer. Plants are the most familiar primary producers in our daily lives using photosynthesis to convert sunlight energy into chemical energy and uptaking their nutrients from the surrounding environment. However, plants are accompanied in this role by algae and photosynthetic bacteria. Some organisms, such as the Archaeans that inhabit deep-sea hydrothermal vents, are able to derive their energy from inorganic chemicals rather than sunlight through chemosynthesis.

    Primary Consumers

    • Primary consumers are organisms that feed directly on primary producers. Among animals, these organisms are often termed grazers or herbivores and often feed on plants or algae. While zebras, giraffes and cattle may easily come to mind as primary consumers, many primary consumers are much smaller, such as insect pests of crops. The energy and nutrients absorbed from the primary producers is incorporated in the cells and tissues of the primary consumer which, in turn, may become the food source for subsequent trophic levels.

    Secondary, Tertiary and Quarternary Consumers

    • Secondary Consumers feed on primary consumers and are exemplified by predator-prey relationships and would also apply to parasites of primary consumers. The food and nutrients needed by secondary consumers is obtained through the flesh and tissue of the primary consumer. Some secondary and subsequent trophic level consumers are considered keystone species since their feeding habits may control the populations within the ecosystem. Tertiary consumers feed on other predators. These tertiary consumers may, in turn, be fed upon other consumers, known as quartenary consumers. Sea urchins feeding on kelp, a primary producer, would be primary consumers. Sea otters feeding on the sea urchins would be secondary consumers. In kelp forests, sea otters are considered a keystone species since they control the sea urchin population, which could destroy the kelp forest if left unchecked.

    Decomposers

    • Decomposers break down the waste material of organisms releasing the nutrients to the environment where they may again be taken up again by primary producers and into the subsequent food web. The food web is more complex, as a succession of decomposers may break down waste material and the decomposers themselves may become prey for other consumers. Decomposers are often associated with fungi and bacteria, but a number of insects and other animals play a significant role in decomposition.


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