This term was first introduce by Tansely in 1935 AD.

Eco systems are of two types:

1. Natural Ecosystem
2. Artificial Ecosystem

In artificial ecosystems like aquarium, man made Forests and Ponds, the equilibrium is controlled by human beings.

Many naturally occuring ecosystems are inter related and collectively form the largest known ecosystem or the living plant of our universe, it is called Biosphere. It consist of surface of earth, water and atmosphere or air capsule along with all animals, plants and micro-organisms.

In every ecosystem interaction exists between living things and non living things. Due to this fact, ecosystem is divided into two components:

1. Living or Biotic Component
2. Non Living or A-Biotic Component

According to the mode of nutrition, living things are grouped into two types:

1. Autotrophs
2. Heterotrophs

Generally they are green plants containing chlorophyll and produce starch by means of Photosynthesis.

They are generally non green fungi, bacteria, animals etc.

Living or Biotic components of an ecosystem can also be classified on the basis of production and consumption of food. According to this classification, living beings are of three types:

1. Producers
2. Consumers
3. Decomposers

They are capable of converting sunlight (Radient energy) into chemical energy (food i.e. glucose). They also serve to equilibrate between certain inorganic compounds. For example organic and biotic compounds by converting CO₂ and H₂O into Glucose and other substances.

They are not capable of preparing their own food material and therefore totally depend upon Producers.

Consumers are further classified into three groups:

1. Primary Consumers
2. Secondary Consumers
3. Tertiary Consumers

These are herbivores and are totally depended upon producers i.e. green plants. This wide group includes Grasshopper, Dragon flies, Leaf hoppers, Caterpillars like arthropods to large animals like Sheep, Goat, Camel, Cow and Buffalo. In aquatic habitat crabs, lobsters, herbivore fishes and prawn belong to this category.

These are carnivore animals, which feed upon Primary consumers or herbivores. For example carnivorous fishes, insectivorous, certain small predators and omnivorous lie Rat etc.

These are higher predators, which feed upon other primary or secondary consumers but in turn are not eaten up by others. For example hawk preys fishes, owl and eagle prey rats, Lion preys deer and Zebra etc but these predators are no preyed by the othes.

It is the most important group of ecosystem, which is composed of microscopic organisms like bacteria, protozoa and Fungi. Most of them are Saprophytes while a little of them are also parasites. They act upon remains and dead bodies of all living components and convert them into simpler organic and Inorganic substances. In this way decomposers are necessary for recycling of substances.

For example air, water, soil and minerals etc.

These components are of two types

1. Materials
2. Energy

Materials are the organic and inorganic substances like elements, compounds, Proteins and carbohydrates etc.

Energy is mainly is of Radiant type like light and heat. Energy of an ecosystem is conserved and changes from one form to another. Similarly materials are also in an equilibrium and in a process of cycling called bio-chemical cycles.

Abiotic components affect an ecosystem, by means of three factors:

1. Climate factors
2. Topographic factors
3. Edophic factors

These are light, air, temperature, water and wind velocity.

As we know that light is a form of Radiant energy and consists of seven colours. It is essential for the synthesis of food materials by the green plants i.e. photosynthesis. It affects by means of its intensity, duration and quality.

Intensity of light varies with seasons, attitude and time while Photoperiochism i.e. flowering, growth and fruiting depends upon duration of light. Animal migration, reproduction and hibernation also depends upon duration i.e. length of day. In terms of quality, the ultra violet light destroys microorganisms of an ecosystem.

Life on earth mainly exists in temperature range of O° to 50° C. Therefore variation of temperature results in the death, growth, dormancy etc of living beings of an ecosystem.

It is a raw material for the synthesis of food during photosynthesis. Therefore availability of water greatly influences the type, growth and various physiological functions of living component. Plants are even classified on the basis of water availability.

Atmosphere contains different gases such as CO₂, O₂, N₂ etc in different concentrations at different altitudes. Wind circulates these gases along with water vapours and therefore they combinely alter the morphology as well as Physiology of living components.

It is responsible for sudden changes in an ecosystem by altering the composition of non-living substances.

It the study of surface texture of earth. Topographically, earth can be recognized to have patches, grounds, slopes and steeps. The altitude greatly influences the temperature, duration and quality of sunlight, wind velocity and water contents. Topographic factor is themain cause of Zonation of earth into different Biomes.

Type, condition and composition of soil are the Edaphic factors. Soil is formed due to weathering of rocks. It contains inorganic salts i.e. minerals and organic matter obtained from the decay of dead plants, animals and their fuselage.

Soil particles range from 0.002 mm up to 2 mm in size. Gases can enter through the pores or gaps between the soil particles and therefore there is a constant exchange of gases between underground parts of plants, under ground animals and micro organisms and atmospheres.

Fertility of soil, which affects the growth of plants depends upon the presence of Organic matter in the soil. The under decomposed organic matter is called Littre while fully decomposed matter is called Humus. These substances along with water contents of soil greatly influence the fauna and flora of an ecosystem. The main difference of different Biomes greatly depend upon the Edaphic factor.

Habitat is further divided into two:

1. Terrestrial Habitat
2. Aquatic Habitat

Terrestrial habitat is divided into different climatic regions or Biomes. On the other hand aquatic habitat is further grouped into three:

1. Fresh Water Habitat (Ponds, Lakes and Rivers)
2. Marine Habitat (Oceanic Habitat)
3. Estuarine Habitat (where River meets Sea)

It is the habitat of ponds, lakes, swamps and Rivers. It is further classified into following:

1. Lentic
2. Lotic

It is non-flowing or standing water generally found in lakes, ponds, ditches and swamps. The fauna and flora of this water are influenced by the depth, light minerals and temperature.

Lentic water can be divided into three zones according to punctuation of light, these are:

1. Littoral Zone
2. Limnetic Zone
3. Profaned Zone

It is illuminous or lighted zone in which light easily penetrates. It may be defined into marginal, shallow and deeper zones. The Peripheral or marginal zones (bank) contains amphibious plants, animals, certain larvae etc. The shallow zone i.e. up to 3 meters depth contains partially submerged plants like Lotus, Lily, Hyaeinth and Ranumculus etc. Their roots lie in mud while leaves float or surf. Animals are Zooplanktous, protozoa and certain invertebrate.

The deeper zone contains submerged plants like Hydrilla, Trapa, Vallisneria, Potamogaton etc. Animals are zooplanktons, worm, Leech, Vertebrates like fishes, frogs, lizards etc. Phytoplass are evenly distributed in all zones.

It is up to 8 meters in depth, here intensity of light is very low therefore heavy vegetation is not present. Certain free floating algae like Oscillatoria, Spirogyne and Stergeocoloneum are formed. Phyto and Zoo planktons are present. Animas are fishes, arthropods etc.

It is the dark zone below 8 meters. It is devoid of vegetation. However it, is rich in decomposers like bacteria and fungi and the decomposed or under decomposed organic matter of dead bodies of animals and plants.

It is the running fresh water. It contains low oxygen than lentic water. Animals and plants face difficulty in respiration and speed of water currents.

Plants develop advance root system for effective anchorage and not for absorption of water. Leaves are small, reduced or much dissected to produce least resistance against water converts. Stems are spongy and soft to store air for respiration.

Animals are generally smaller in size and spindle shape. Most of them are provided with hooks, hold fasts and suckers to adhere with rocks. Animals are generally sponges, certain arthropods, molluscus and fishes.

It is also called Oceanic Habitat. The marine water is saline i.e. contains 3.5% salts, temperature is about 32° C. Animals and plants adapt accordingly to survive. Oxygen contents at different depths also varies, generally surface water moves towards the coasts and deep water rises to the surface, which is called Up Welling.

Marine habitat can be divided horizontally as well as vertically.

Horizontally sea can be divided into coastal and shallow Neretic Zone and deeper Oceanic Zone.

It starts from coastal margin up to the depth of 180 meters generally. It is further divided into:

1. High Tidal Zones
2. Inter Tidal Zones
3. Low Tidal Zones

The high tidal zone remains exposed except few days of months. Intertidal zone remains exposed in low tides and covers with water during high tide. Low tidal area generally forms water covered oceanic floor.

Neretic zone is the most productive area. Water of this area contains more oxygen, carbon dixoide and sunlight as compared to oceanic zone.

The deep sea is called oceanic zone. In this area vegetation is less.

Vertically mrine habitat is dived into three major zones i.e.

1. Euphotic Zone
2. Bathyal Zone
3. Abyssal Zone

It is illuminated zone where sunlight can enter. It is up to 200 meters in depth. The whole neretic zone lies in this area. Vegetation is thick and productivity is high.

It is the aphotic or darker zone and reaches the depth of 2000 meters. Bathyal zone lies in the oceanic area and further divided into Pelagic Zone and Banthic Zone.

It is the deepest part of oceanic zone and is below 2000 metes in depth. Due to absence of light, it is devoid of vegetation. However it is rich in organic matter, shells decomposers and scavenge small fishes with large mouth are also present.

Neretic zone is rich in green vegetation, Phytoplanktous, distance and algae. Animals are mostly moluscs, Arthropods and small fishes. In sub tidal or deeper neretic zone Phytoplanktous, molluscs, Echimoderms and Protozoans, arthropods, vertebrates like fishes, seals and whales are found.

In oceanic region, Euphotic zone contains large number of Phytoplanktous, whales and fishes. Ephotic zone contains filter feeders. In Abyssal zone plants are absent and animals are mostly scavengers. However population of Bacteria and fungi is high.

In a natural ecosystem, equilibrium exists between biotic and abiotic components. Different element recycle and their composition remains constant. Some of the cycles are given below:

In an ecosystem, carbon exists in different forms i.e. carbonates, carbohydrates and CO₂. Free carbon exists in the form of coal.

Producers i.e. green plants convert CO₂ into carbohydrates and Proteins or lipids by means of photosynthesis. The foodstuff prepared by plants are taken up by consumers. They oxidize these food components in respiration and convert it into CO₂. However a part of it converts into living body components and trapped in cells of consumers and producers. Death of these living beings leads to decomposition of their bodies by Decomposers which convert them into compounds like carbonates CO2, Bicarbonates and coal. Oxidation of these substances yields CO₂, which reaches in air.

Hydrogen is found in a compound state i.e. H₂O in an ecosystem. Plants absorb water from soil, rain, lakes, rivers and sea water is utilized in Photosynthesis and other vital activities of plants and animals. During respiration, oxidation of food yields H₂O vapours, which is liberated in air, here vapours condense to form clouds and water again reaches the sides and reservoir during rain. Decomposition of dead bodies of living beings also liberate water with again reaches the soil.

Oxygen is found in free state i.e. O₂ in air, which is constantly consumed by all living beings during respiration. Plants produce O₂ gas during photosynthesis, which again reaches in air.

In this way carbon Hydrogen and oxygen constantly recycle in an ecosystem.

In air, Nitrogen is abundantly found in free state, its concentration varies from 76 to 79 parts. Organismsm like symbiotic nitrogen fixing bacteria, which are found in Nodules of legumes roots, absorb this nitrogen from air. Similarly certain blue green algae like Nostoc also absorb nitrogen. Both of them convert N₂ into soluble Nitrites and Nitrates. These compounds are absorbed by the plants in which they are converted into proteins. Some of the plant protein is taken up by the animals where it is converted into animal protein and get trapped. A small portion of it is excreted by the animals, which is acted upon by the putrefying bacteria.

Death of animals and plants leads to conversion of their bodies into nitrates and nitrites by the putrefying bacteria. Some of the amount is absorbed by the plants while rest is converted into Ammonia and Nitrogen gas.

Thundering and rain converts N₂ and Ammonia into nitrates and nitrites which again reach the soil and thus whole cycle is repeated.