The study of an ecosystem is not only a description of the biotic community and its abiotic environment. It involves the whole network of relationship comprising various exchanges between the living and nonliving components. The various structural components of an ecosystem are classified under two main groups.
1. Biotic Components (Living Components)
The biotic or living components of the ecosystem comprise the kinds, numbers and distribution of living organism. All organisms require energy for their life processes and materials for their formation and maintenance of body structures. Food supplies both energy and materials for sustenance of life. Green plants produce carbohydrate by photosynthesis and also synthesise fats and proteins.
The green plants are called producers and the animals that consume this energy of food are called consumers. The non- green organisms like the fungi and bacteria which are incapable of producing their food are called consumers. They live on the dead and decaying plants or animals parts.
The communities of green plants-which absorb carbon-dioxide, mineral nutrients, water and built up organic matter with the help of a solar energy, are called producers. Producers release oxygen and thus life activity in the system will collapse in the absence of producers.
They are also called as autotrophic organisms.
These autotrophs are of two types:
(i) Photoautotroph’s: Which contain green photosynthetic pigments chlorophyll to transduction the solar or light energy of sun e.g. trees, grasses, algae, bacteria and cyanobacteria.
(ii) Chemoautotroph’s: Which use energy generated in oxidation reduction processes e.g. sulphur bacteria etc?
Amongst the producers only the green plants and some special type of bacteria which can trap solar energy and produce food are called primary producers. The heterotrophs which are food for other animals become secondary producers.
All other animals that do not make their own food but depend on other organisms to obtain their energy for survival these are called heterotrophs or consumers. Among consumers some animals such as goat, cow, deer, rabbit and insects which eat green plants are called primary consumers or herbivores. Organisms which eat herbivores like a frog that eat grasshoppers are called secondary consumers. Organisms which eat these secondary consumers are called tertiary consumers.
The primary consumers are herbivores but the secondary and tertiary consumers are called carnivores. However, animals are known as top carnivores.
A chain of organism based on trophic relationship is established which is known as food chain. The energy trapped by green plants is released to be used by consumers when organic matter is degraded oxidised. Oxygen is used and CO is released in the process. In a complicated ecosystem, there may be several interlinked food chain and the trophic structure assumes the shape of a complicated food web.
Consumers may be classified into two classes which are summarised as:
(a) Macro-consumers: Macro-consumers include herbivores, carnivores and omnivores. The herbivores are also known as primary consumers, carnivores as secondary consumers and omnivores as tertiary consumers.
(b) Micro-consumers: Organic materials are added to the environment with the death of plants and animals and also due to deposition of animal’s waste products. Such organic materials are decomposed by micro-organisms, i.e. known as decomposers.
Faecal matter, exudates and excreta of plants, animals and their dead bodies are decomposed by the activity of bacteria, fungi and other small organisms which live on dead and decaying organic matter. They constitute the community of decomposers which bring the constituent elements of the plants and animals bodies back to the surrounding medium or to the soil.
The role of decomposers is very special and important. Certain decomposers are also called scavengers.
II. ABIOTIC OR NON-LIVING COMPONENTS
All the abiotic factors or non-living factors are not known as yet and the implications of many have not been understood adequately. Abiotic components of the ecosystem are of three types:
(i) Climatic System:
Climatic conduction as well as physical factors of the given region e.g. air, water, soil, temperature, light, moisture, rainfall etc.
(ii) Inorganic substances:
Inorganic substances e.g. carbon, nitrogen, sulphur, phosphorus, hydrogen etc all of which are involved in geochemical cycle.
(iii) Organic Substances:
The major organic substances e.g. proteins, carbohydrates, lipids, humic substances which are present either in the environment or in biomass. The biochemical structure links the biotic and abiotic compounds of the ecosystem.