The various communities of living organisms (plants and animals) interact among themselves as well as with their physical environment like soil, air and water. The living organisms interact with one another through their food chains in which one organism consumes another organism.
The living organisms like plants interact with soil to get essential nutrients like nitrogen, phosphorus, etc.; with air to get carbon dioxide and also with water bodies, for carrying out the process of photosynthesis. Thus, the various communities of living organisms (called biotic communities) like plants and animals along with soil, air and water of that region form a self-sustaining or functional unit of the living world.
This ‘functional unit’ or ‘system’ made up of living and non-living components which is capable of independent existence is called an ecosystem. The ecosystem includes all the communities of an area (all the plants and animals of an area) functioning with their non-living environment like soil, air and water. We can now define an ecosystem as follows.
An ecosystem is a self-contained unit of living things (plants, animals and decomposers), and their non-living environment (soil, air and water). An ecosystem needs only the input of sunlight energy for its functioning. The examples of ecosystems are: a grassland (meadow); a forest; a desert; a mountain; a pond; a lake; a river; and sea.
When we say that a pond or lake is an ecosystem, then the word pond also includes all the aquatic life (plants and animals) which occurs in this pond water. This is because the living organisms are found everywhere. Similarly, when we say that a forest is an ecosystem then it means the physical environment of the forest like soil, air and water along with all the plants and animals which occur in the forest.
The desert, grassland, forest, cropfield and mountains represent terrestrial ecosystems (land- based ecosystems) whereas ponds, lakes, river, sea and aquarium represent aquatic ecosystems (water- based ecosystems).
Most of the ecosystems in the world are natural ecosystems but some of them are also man-made ecosystems or artificial ecosystems. The examples of artificial ecosystems are crop-fields (agricultural lands); gardens; parks and aquarium.
Components of an Ecosystem:
All the ecosystems are made up of two main components: Abiotic components, and biotic components. Biotic components mean non-living components and biotic components mean living components. Thus, we can now say that an ecosystem consists of non-living environment and the living biological community.
1. Abiotic Components of an Ecosystem:
The abiotic components of an ecosystem (or the non-living components of an ecosystem) include the physical environment like soil, water and air along with the inorganic substances like carbon dioxide, nitrogen, oxygen, water, phosphorus, sulphur, sodium, potassium, calcium and other elements present in them. The physical factors or climatic factors like light, temperature, pressure and humidity are also considered abiotic components of the ecosystem.
2. Biotic Components of an Ecosystem:
The biotic component of an ecosystem (or the living component of an ecosystem) is a community of organisms (like plants and animals), which is made up of many different inter-dependent populations. The biotic community (or living community) of an ecosystem includes three types of organisms:
(i) Producer organisms (or Autotrophs) which synthesize their own food. All the green plants are producers.
(ii) Consumer organisms (or Heterotrophs) which are dependent on others for food. All the animals are consumers.
(iii) Decomposer organisms (or Saprotrophs) which consume the dead remains of other organisms. Certain bacteria and fungi are decomposers.
We will now describe how an ecosystem functions as a self-sufficient or independent unit in nature.
We have just discussed that an ecosystem has non-living components like soil, water and air which contain inorganic nutrient elements, and the living components called producers, consumers and decomposer organisms. All these components make the ecosystem function as follows:
From the nutrient pool of the earth (soil, water and air), carbon dioxide and water are absorbed by the producer organisms (green plants). With the help of sunlight energy, the producer organisms convert these inorganic substances into organic compounds like carbohydrates which act as a food.
Thus, producers trap the solar energy and then provide the basic food or energy for all other life forms in the ecosystem. The consumers (animals) derive their energy needs, directly or indirectly, from producers (plants).
When the producers (plants) and consumers (animals) die, then the decomposer organisms act on their dead bodies to return the various elements back to the nutrient pool (soil, water and air). Thus, an ecosystem involves input of energy and matter which are exchanged between living and non-living components in a cyclic process.