According to the manner in which they obtain their food from the environment, all the organisms can be divided into three groups: producers, consumers and decomposers.
Those organisms which produce food are called producers. Producers are the organisms which can prepare their own food from simple inorganic substances like carbon dioxide and water by using sunlight energy in the presence of chlorophyll.
The examples of producers are green plants and certain blue-green, algae. The green plants synthesize their food during photosynthesis by taking raw materials from the earth and energy from the sun maize (makkd) as food.
The green plants produce carbohydrates by photosynthesis and also synthesize proteins and fats. Thus, the green plants are called producers in the living world. Producers are the autotrophic organisms (self- feeder organisms) in the ecosystem upon which other organisms depend for food. Thus, producers (like green plants) are autotrophs.
Those organisms which consume food (eat food) prepared by producers are called consumers. The consumers depend on producers for food, directly or indirectly. The consumers get their food by eating other organisms or their products. In most simple words, consumers .are the organisms that eat other organisms.
All the animals are consumers. Even the microscopic animal lives of the water called protozoa are consumer organisms. The examples of common consumer organisms are man, goat, deer, fish, lion, cow and buffalo, etc. The cow and buffalo eat green grass and other green fodder because green grass and other green plants are producers of food.
The bio-mass of grass and plants supplies food and energy to these animals like cow and buffalo. It should be noted that the consumer organisms like animals cannot prepare food from simple inorganic substances through photosynthesis.
The consumers need ready-made food for their survival which they get from producers (green plants), either directly or indirectly. If an animal eats grass or other green plants or their products itself we say that it gets the food from producers directly.
For example, a goat gets the food from producers directly when it eats grass. On the other hand, if an animal eats the meat of another animal (which eats grass), then we say that it gets the food from producer indirectly. For example, a lion gets food by eating goat which in turn eats grass. So, in this case the lion gets its food indirectly from producer grass (through the goat). Consumer organisms are also called heterotrophs. Consumers can be further divided into three groups: herbivores, carnivores and omnivores.
Some animals eat only plants (or their products). Those animals which eat only plants are called herbivores. The herbivores may eat grasses, leaves, grains, fruits or the bark of trees. Some of the examples of herbivores are: Cow, Buffalo, Goat, Sheep, Horse, Deer, Camel, Ass, Ox, Elephant, Monkey, Squirrel, Rabbit and Hippopotamus. Cow is called an herbivore because it eats only plants (or plant products) as food. Herbivores are also known as herbivorous animals.
The animals which get their food by eating the producers (plants) directly are called primary consumers. Since herbivores obtain their food directly from plants (or producers), therefore, herbivores (like cattle, deer, goat, etc.) are primary consumers.
Some animals eat only other animals. They do not eat plant food at all. Those animals which eat only other animals as food are called carnivores. The carnivores eat the meat (or flesh) of other animals.
So, we can also say that those animals which eat only the meat (or flesh) of other animals are called carnivores. Some of the examples of the carnivores are: Lion, Tiger, Frog, Vulture, Kingfisher, Lizard, Wolf, Snake and Hawk. Lion is called a carnivore because it eats only the meat (or flesh) of other animals like deer, rabbit and goat, etc. Carnivores are also known as carnivorous animals.
The carnivores are usually of two types: small carnivores and large carnivores. The small carnivores which feed on herbivores (primary consumers) are called secondary consumers.
For example, a frog, lizard, bird and fox, etc., are secondary consumers. The large carnivores (or top carnivores) which feed upon the small carnivores (secondary consumers) are called tertiary consumers. For example, lion, tiger and birds of prey (such as hawk) are some of the tertiary consumers. Please note that humans (man) can be primary, secondary or tertiary consumers depending on the food which they eat.
Some animals eat both, plants as well as other animals. Those animals which eat both, plants and animals are called omnivores. In other words, the omnivores eat plant food as well as the meat (or flesh) of other animals. Some of the examples of omnivores are: Man (human beings), Dog, Crow, Sparrow, Bear, Mynah and Ant. Man is called an omnivore because he eats both, plant food (such as grains, pulses, fruits and vegetables) as well as meat of animals (such as goat, chicken and fish). Omnivores are also called omnivorous animals.
We will now describe another type of producers and consumers which are extremely small. These are called planktons. Planktons are very minute or microscopic organisms freely floating on the surface of water in a pond, lake, river or ocean. Planktons are of two types: Phytoplanktons and Zooplanktons.
The microscopic aquatic plants freely floating on the surface of water are called phytoplanktons. The free-floating algae are an example of phytoplankton. Phytoplanktons are capable of producing food by the process of photosynthesis. The microscopic aquatic animals freely floating on water are called zooplanktons.
The freely-floating protozoa are an example of zooplankton. A very, very small fish is also a zooplankton. Planktons float near the surface of water and provide food for many fish and other aquatic animals.
The non-green micro-organisms like some bacteria and fungi, which are incapable of producing their food, live on the dead and decaying (rotting) plants and animal bodies and are consumers of a special type called decomposers.
We can now say that: The micro-organisms which break down the complex organic compounds present in dead organisms like dead plants and animals and their products like faeces, urine, etc., into simpler substances are called decomposers. The examples of decomposers are certain bacteria and fungi.
The bacteria which act as decomposers are called putrefying bacteria. The bacteria and fungi act as decomposers by the secretions of their body surfaces which decompose the organic matter present in dead plants and animals into simpler substances and liberate ammonia, carbon dioxide, etc.
They absorb some of these simpler substances for their own maintenance and release the remaining into the soil, water and air to be used by the producers again In this way, decomposers help in the recycling of materials in ecosystem. The decomposers are also known as micro-consumers or saprotrophs.
Importance of Decomposers:
The decomposers help in decomposing the dead bodies of plants and animals, and hence act as cleansing agents of environment. The decomposers also help in putting back the various elements of which the dead plants and animals are made, back into the soil, air and water for re-use by the producers like crop-plants.
This maintains the fertility of soil and the soil would continue to support crops again and again. For example, the decomposers like putrefying bacteria and fungi decompose the dead plants and animal bodies into ammonia (and other simpler substances).
This ammonia is converted into nitrates by the nitrifying bacteria present in soil. These nitrates act as fertilizer in the soil and are again absorbed by the plants for their growth. Thus, it is only due to the presence of decomposers that the various nutrient elements which were initially taken by plants from the soil, air and water are returned to the soil, air and water, after the death of plants and animals.
If, however, there were no decomposers, then the dead bodies of plants and animals would keep lying as such and the elements of which plant and animal bodies are made, would never be returned to their original pools like soil, air and water. In that case, the cyclic process of life and death would be disrupted.
This is because in the absence of decomposers the soil, air and water would not be replenished by elements from the bodies of dead organisms. All the nutrients present in soil, air and water would soon be exhausted and evolution of life would come to an end. Thus, the decomposer organism's help in recycling the materials in the ecosystem so that the process of life may go on and on like an unending chain.