- The branch of science that deals with the study of structures and functions of nature and the environment is called ecology. In other words, it is the study of relationship between organisms and their environment.
- Ecosystem can be defined as a self-sustaining structural and functional unit of biosphere consisting of a community of organisms and the physical environment.
- An ecosystem can be both natural and artificial. Grassland, pond, desert, forest, sea etc. are some examples of natural ecosystems whereas aquarium, park, crop-field etc. are artificial ecosystems.
- An ecosystem consists of two components:
A. Abiotic components: They are the non-living components of the ecosystem which include;
- Physical environment:
- Edaphic components like soil, water, air and topography.
- Inorganic components like oxygen, carbon dioxide, water, nitrogen, sodium, potassium, calcium, phosphorus etc. which are responsible for the recycling of materials in an ecosystem.
- Organic components like carbohydrates, proteins, lipids etc. which form the living body and connect abiotic and biotic components together.
- Climatic factors:
- They include sunlight, temperature, moisture, humidity, rainfall, air pressure etc. which affect the distribution, number, metabolism and behavior of organisms.
B. Biotic components: They are the living components of an ecosystem and hence include all the living organisms present in that ecosystem. On the basis of nutritional relationship, biotic components of an ecosystem are classified into:
- Producers:
- They are chlorophyll bearing plants which can prepare their own food by the process of photosynthesis and hence are called autotrophs.
- Green plants use carbon dioxide and water in the presence of sunlight and chlorophyll to synthesize glucose (food).
- This chemical energy is stored in the form of starch.
- Consumers:
- They are the heterotrophic animals that depend on green plants directly or indirectly for food.
- On the basis of nature of food, consumers are divided into three categories.
a. Primary consumers:
- The consumers that feed directly on green plants or autotrophs are called primary consumers.
- They are also called herbivores.
- Protozoans, crustaceans, molluscs, zooplanktons etc. are some examples of primary consumers in an aquatic ecosystem.
- Similarly, grasshopper, rabbit, deer, goat, elephant, cattle etc. are some primary consumers in a grassland ecosystem.
b. Secondary consumers:
- Secondary consumers are carnivorous animals that feed on herbivores and some are omnivorous.
- They are indirectly dependent on green plants and provide food for tertiary consumers.
- Fish, frogs, snakes, birds, dog, fox etc. are some secondary consumers.
c. Tertiary consumers:
- The consumers that feed on secondary consumers as well as primary consumers are called tertiary consumers.
- They are strict carnivores.
- Tiger, lion, owl, crocodile, sharks etc. are tertiary consumers.
- Decomposers:
- They are saprophytic organisms that feed on dead bodies of organisms and decaying organic matter.
- They decompose the complex organic compounds present in the dead bodies into simpler substances.
- Bacteria and fungi are the examples of decomposers.
- They are responsible for regular cycling of materials in an ecosystem between the living and non-living components.
- Through the decomposers, the elements enter the earth again, which in turn, are again taken up by the autotrophs.
Role of decomposers in an ecosystem:
- Decomposers break down the dead bodies of plants and animals into simpler forms.
- They help in recycling the materials in the environment between the living and non-living components of the ecosystem.
- Decomposers also maintain the fertility of the soil.