The term eco-system is coined by combining two words “Eco” which means the environment and ‘system’ means a set of interacting inter-dependent living and non-living (inorganic or abiotic) components. A. G. Tanslay (1935), for the first time, suggested the term “Eco-system” which he defined as “the system resulting from the integration of all living and non-living factors of the environment”.
According to him, “it has both structure and function”. The structure tells about the species diversity and the function involves the flow of energy and cycling of materials through the structural components. In 1954, Woodbury defined eco-system as a complex in which the living organisms and environment form an interesting unit where material and energy of one can easily pass in and out of other.” According to E.P. Odum (1968), eco-system is the basic functional unit of organisms and environments interacting with one another and with their own components.
Thus, an organisation that includes all the living organisms in a given area, interacting with its physical environment and initiating a flow of energy which leads to a clearly well defined trophic structure, biotic diversity and material cycle (i.e., exchange of materials and energy in between living and non-living components) within the system, is known as eco-system. In short, an eco-system is a system of organisms functioning together with their non living environment.
An eco-system may be as large as an ocean, forest, desert etc. or as small as a crop land, a pond etc. These unit eco-systems are linked with each other forming an integrated whole though these are separated by time and space.
The largest eco-system of earth is biosphere which is balanced and self-sufficient. Highest level of ecological integration is seen in eco-system which is energy based and the functional units are capable of energy transformation, accumulation and circulation.
Kinds of Eco-System:
There are several types of eco-systems. Together they constitute the giant eco-system or biosphere.
The different kinds of ecosystems are:
(i) Natural eco-system.
(ii) Terrestrial (forest, grassland, desert) eco-system.
(iii) Aquatic (water-open) eco-system.
(iv) Artificial (man-made) eco-system.
The aquatic eco-system may be further sub-divided into:
(a) Running fresh water (may be running water like spring, stream river)
(b) Standing fresh water (may also be standing water like Lake, pond, pools, swamp etc.).
(c) Marine water (deep sea).
Components of Eco-System:
The structure of an eco-system describes the composition of biological community, physical features of environment including the quantity and distribution of nutrients in a particular habitat and climatic conditions prevailing in the area.
From the structural point of view, each eco-system has two basic components:
1. Biotic component.
2. Abiotic component.
From the functional point of view, each eco-system has two basic components:
(a) Autotrophic component
(b) Heterotrophic component.
Odum (1971) had divided eco-system into six different phases:
(i) Inorganic components e.g., carbon, nitrogen, carbon- dioxide, water etc.
(ii) Organic components e.g. protein, carbohydrate, lipid, etc.
(iii) Climatic regime e.g. temperature, light and other physical factors.
(iv) Producers e.g. Autotrophic organisms, green plants.
(v) Macro-consumers or phagotrops e.g. mainly animals.
(vi) Micro-consumers e.g. mainly bacteria and fungi.
The biotic components include all the living organisms present in the environmental system. The living organisms are distinguished on the basis of nutritional relationship (food preparation and food dependency).
Hence, on the basis of nutrition point, biotic component can be further sub-divided into two sub-components:
(a) Autotrophic components
(b) Heterotrophic components
(a) Autotrophic Components:
(Auto means self; troph means nourishing)
The autotrophic components include green plants, photo- synthetic bacteria, chemosynthetic microbes etc. The members of autotrophic components are known as producers.
Basing on the size of the producers, these are of two types:
(a) Micro Producers (Microscopic): Phytoplankton’s, algae, etc.
(b) Macro Producers (Macroscopic): Green plants, grasses, etc.
The main function of producer is to absorb energy from nonliving environment and make it available to all living organisms. That is, the producers absorb solar energy through light trapping pigments, chlorophylls and prepare complex organic compounds (where energy is stored in the form of potential chemical energy) with the help of inorganic substances like water and carbon dioxide from environment. Such a process is known as photosynthesis, carbon-assimilation or primary biological productivity. In addition, oxygen is evolved which is used in respiration by all
Besides the production of food, the main function of producers is to convert solar energy into chemical energy. E.J. Kormondy replaced the term producer by convertor or transducer. ,
(b) Heterotrophic components:
(Hetero means different: troph means nourishing)
These are the living organisms which are unable to prepare their own food but these consume, rearrange and decompose the complex food material prepared by the producers.
Heterotrophs are of two types:
(b) Decomposers and transformers.
The living organisms which consume the food prepared by the producers are known as consumers.
Basing on dependency, these are classified into the following categories:
(i) Primary consumers or consumers of first order.
(ii) Secondary consumers or consumers of second order.
(iii) Tertiary consumers or consumers of third order.
(iv) Parasites, scavengers and saprobes.
(i) Primary Consumers:
These are purely herbivorous animals, i.e. these are dependent for their food on green plants. Some common examples are cow, buffalo, goat, deer, rabbit, rodents, insects, etc. of terrestrial eco-system and small crustaceans, molluscs, etc. of aquatic ecosystem. In the year 1939, Elton suggested the herbivorous of eco-system as key industry animals.
(ii) Secondary Consumers:
These are carnivorous (organism eating herbivores) and omnivorous (organism eating both herbivorous and carnivorous). Some common examples are fox, wolves, dogs, cats, snakes, etc.
(iii) Tertiary Consumers:
These are the top carnivores which feed on other carnivorous, omnivorous and herbivorous. Some common examples are lions, tigers, hawks, vultures, etc.
(iv) Parasites, Scavengers and Saprobes:
The parasitic plants and animals feed on living tissues of different plants and animals. The scavengers and saprobes consume dead animals and plants as their food.
(a) Decomposers and Transformers:
These are the living organisms of eco-system which constantly decompose organic substances in dead organisms and derive food and energy from them. These are some micro-organisms like bacteria and fungi. The decomposers attack the dead bodies of consumers and producers and degrade the complex organic substances into simpler compounds.
Then the transformers convert these simple organic matters into inorganic forms that are suitable for reuse by producers. The decomposers and transformers are very important micro-organisms which maintain the dynamic nature of the eco-system.
This component includes non-living part of the eco-system. The non-living substances enter the body of living organisms, participate in different physiological activities like metabolism and finally return to the environment.
The abiotic component of ecosystem can be divided into three parts:
(a) Inorganic Components:
A variety of basic inorganic substances like soil, water, oxygen, carbon dioxide, calcium carbonate, phosphate etc.
(b) Organic Components:
A variety of organic substances usually the byproducts of different organic activities like proteins, carbohydrates, lipids, humic substances etc.
(c) Physical Components:
These are the various environmental factors like light, temperature, humidity, etc. There exists a direct link in between abiotic and biotic components. The constituents are in continuous cycle from the environment into the living organisms and from the organisms by death and decay into the environment.
This cycle is known as bio-geo-chemical cycle. Similarly, the solar energy is continuously trapped by the producer from the sun and energy is released via respiration and heat loss into the space. A schematic representation of a generalized eco-system showing stores (where processing takes place), inputs and outputs is given in Fig. 3.2.