Relationships Of Organisms In An Ecosystem

An ecosystem is a basic functioning unit of nation. It is made up of living organisms and their non-living environment. Both components, not only interact among themselves, but are also linked by a variety of biological, chemical and physical processes. We shall now study relationships of organisms in an ecosystem which result in the ecosystem being a functioning unit.

Autotrophs and Heterotrophs
The basic component of an ecosystem is made up of all the living organisms in it. These organisms are divided into two main groups according to the way they feed; autotrophs and heterotrophs.


Autotrophs are organisms that are able to use sunlight or chemical energy to manufacture their own food from simple inorganic substances.
   Autotrophs extract inorganic nutrients and chemical energy from their non-living environment, that is from the abiotic  component of the ecosystem. Sunlight, the main energy source used by autotrophs, is obtained from the sun which is outside the ecosystem. By being able to use sunlight, these autootrophs forms a direct link between abiotic and biotic components of an ecoosystem. Since autotrophs are the only oorganisms that can produce food in an ecosystem, they are also known as primary food producers.
        Autotrophs use some food they produce for their activities and building their body tissues (growth). The rest is stored in various parts of their bodies.
       Autotrophs include all green plants, photosynthetic protists and some bacteria. In a terrestrial ecosystem, the main food producers are green plants especially flowering plants such as maize, rice, yam and pawpaw. In an aquatic ecosystem, however, the main food producers are protists like diatoms and algae like spirogyra, often referred to as the phytoplankton. 


Heterotrophs cannot manufacture food. They feed on ready-made food which comes from the tissues of organisms in their environment, that is from biotic component of the ecosystem. This food is produced either directly or indirectly by autotrophs. Thus all heterotrophs depend ultimately on autotrophs for food.
   Heterotrophs use the nutrients and chemical energy stored in the food they feed on for their activities and building up their body tissues (growth). Excess nutrients and energy are often stored in various parts of their bodies.
Heterotrophs include all animals, carnivorous plants, fungi, and most protists and bacteria. In an ecosystem, heterotrophs maybe consumers or decomposers. Consumers are heterotrophs that feed on other organisms. They include

  • all holozoic organisms such as herbivores, carnivores, omnivores and scavengers; and
  • parasites.

Some examples of consumers in a terrestrial ecosystem are caterpillars, cows, dogs, lions, toads, hawks and vipers. The consumers in an aquatic habitat include cope pods, water fleas, tadpoles, larvae of insects and fishes.

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