Ecology is  defined “as a scientific study of the relationship of the living organisms with each other and with their environment.”

The classical texts of the Vedic period such as the Vedas, the Samhitas, the Brahmanas and the Aranyakas-Upanishads contain many references to ecological concepts .The Indian treatise on medicine, the Caraka- Samhita and the surgical text Susruta-Samhita. contain classification of animals on the basis of habit and habitat, land in terms of nature of soil, climate and vegetation; and description of plants typical to various localities.

Caraka- Samhita contains information where air, land, water and seasons were indispensable  for life and that polluted air and water were injurious for health.

The environment is defined as ‘the sum total of living, non-living components;  influences and events, surrounding an organism.

Components of Environment

  1. Abiotic – Energy, Radiation, TEMP, Water, etc.
  2. Biotic- plants, animals, man, DECOMPOSER ETC.

Diesel engine exhaust fumes can cause cancer, humans” and it belong to the same potentially deadly category as asbestos, arsenic and ‘mustard gases.

Six main levels of organisation of ecology are:

  1. Individual- Organism is an individual living being that has the ability to act or function independently.
  2. Population-Population is a group of organisms usually of the same species,

occupying a defined area during a specific time,

  1. Community- Communities in most instances are named after the dominant plant form

(species). A community is not fixed or rigid; communities may be large or small.

Types of Community-

On the basis of size and degree of relative independence communities may be divided into two types-

(a)  Major Community

These are large-sized, well organized and relatively independent. They depend

only on the sun’s energy from outside and are independent of the inputs and

outputs from adjacent communities.

E.g: tropical ever green forest in the North-East


(b) Minor Communities

These are dependent on neighbouring communities and are often called societies.

They are secondary aggregations within a major community and are not therefore completely independent units as far as energy and nutrient dynamics are concerned.

e.g: A mat of lichen on a cow dung pad.

The environmental factors determine the characteristic of the community as well as the pattern of organisation of the members in the community

The characteristic pattern of the community is  termed as structure which is reflected in the roles played by various population, their range, the  type of area they inhabit, the diversity of species in the community and the spectrum of interactions between them

Eco-System-An ecosystem is defined as a structural and functional unit of biosphere consisting of community of living beings and the physical environment, both interacting and exchanging materials between them. It includes plants, trees, animals, fish, birds, micro-organisms, water, soil, and  people.

When an ecosystem is healthy (i.e. sustainable) it means that all the elements live in balance and are  capable of reproducing themselves


Components of Ecosystem

The components of the ecosystem is categorised into abiotic of non-living and biotic of living components. Both the components of ecosystem and environment are same.


  1. Abiotic Components

the inorganic and non-living parts of the world.  consists of soil, water, air, and light energy etc.  involves a ,large number of chemicals like oxygen, nitrogen-, etc. and physical processes including volcanoes, earthquakes, floods, forest fires, climates, and weather conditions.

Abiotic factors are the most important determinants of where and how well an organism exists in its environment. Although these factors interact with each other, one single factor can-limit the range of an organism.


  1. a) Energy

Energy from the sun is essential for maintenance of life. Energy determines the distribution of organisms in  the environment.

  1. b) Rainfall
  2. c) Temperature :-Temperature is a critical factor of the environment which greatly influences survival of organisms. Organisms can tolerate only a certain range of temperature and humidity.
  3. d) Atmosphere :It is made up of 21% oxygen, 78% nitrogen , 0.038% carbon dioxide and other inert gases (0.93% Argon, Neon etc).
  4. e) Substratum :Land is covered by soil and a wide variety of microbes, protozoa, fungi and small animals (invertebrates) thrive in it
  5. f) Materials:

(i) Organic compound

Such as proteins, carbohydrates,  lipids,  humic  substances are formed from inorganic compound on decomposition.

(ii) Inorganic compound

Such as carbon,   carbon dioxide, water, sulphur, nitrates, phosphates, and ions of various metals are essential for organisms to survive.

  1. g) Latitude and altitude

Latitude has a strong influence on an area’s temperature, resulting in change of climates such as polar, tropical, and temperate. These climates determine different natural biomes. From sea level to highest peaks, wild life is influenced by altitude. As the altitude increases, the air becomes colder and drier, affecting wild life accordingly.( wild life decrease as altitude increase)


  1. Biotic Components :Biotic components include living organisms comprising plants, animals and microbes and are classified according to their functional attributes into producers and consumers.

Primary producers – Autotrophs (self-nourishing) Primary producers are basically green plants (and certain bacteria and algae). They synthesise carbohydrate from simple inorganic raw materials like carbon dioxide and water in the presence of sunlight by the process of photosynthesis for themselves, and supply indirectly to other non- producers.

In terrestrial ecosystem, producers are basically herbaceous and woody plants, while in aquatic ecosystem producers are various species of microscopic algae.


  1. b) Consumers — Heterotrophs or phagotrophs (other nourishing)


Consumers are incapable of producing their own food (photosynthesis).

They depend on organic food derived from plants, animals or both.

Consumers can be divided into two broad  groups


(i) Macro consumers- They feed on plants or animals or both and are categorised on the basis of their food sources.

Herbivores are primary consumers which feed mainly on plants e.g. cow, rabbit.

Secondary consumers feed on primary consumers e.g. wolves.

Carnivores which feed on secondary consumers are called tertiary consumers e.g. lions which can eat wolves.

Omnivores are organisms which consume both plants and animals e.g. man.


(ii) Micro consumers – Saprotrophs (decomposers or osmotrophs)


They are bacteria and fungi which obtain energy and nutrients by decomposing dead organic substances (detritus) of plant and animal origin.

The products of decomposition such as inorganic nutrients which are released in the ecosystem are reused by producers and thus recycled.

Earthworm and certain soil organisms (such as nematodes, and arthropods) are detritus feeders and help in the decomposition of organic matter and are called detrivores.

Classification of Eco-system


  1. Natural Ecosystem-

Terrestrial- Forests, Grasslands, Deserts

Aquatic- Fresh Waters, Saline Waters, Marine Waters

Ecotone :- a zone of junction between two or more diverse ecosystems. For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem.

Characteristics of Ecotone

It may be very narrow or quite wide. It has the conditions intermediate to the adjacent ecosystems. Hence it is a zone of tension.

It is linear as it shows progressive increase in species composition of one in coming community and a simultaneous decrease in species of the other out going adjoining community.

A well developed ecotones contain some organisms which are entirely different from that of the adjoining communities.

Sometimes the number of species and the population density of some of the species is much greater in this zone than either community. This is called edge effect For example the density of birds is greater in the mixed habitat of the ecotone between the forest and the desert.



a  description  of  all  the  biological,  physical  and  chemical  factors  that  a  species needs to survive, stay healthy and reproduce. No two species have exact identical niches. Niche plays an important role in conservation of organisms.

Types of Niche

  1. Habitat niche – where it lives
  2. Food niche – what is eats or decomposes & what species it competes with
  3. Reproductive niche -how and when it reproduces.
  4. Physical & chemical niche – temperature, land shape, land slope, humidity & other requirement.


The terrestrial part of the biosphere is divisible into enormous regions called biomes, which are characterized, by climate, vegetation, animal life and general soil type.

No two biomes are alike.

The most important climatic factors are temperature and precipitation.

  1. Tundra- Northern most region  adjoining the ice bound  poles. Devoid of trees except stunted shrubs in the southern part of tundra biome, ground flora includes lichen, mosses and sedges.

The typical animals are reindeer, arctic fox polar bear, snowy owl, lemming, arctic hare,  ptarmigan. Reptiles and amphibians are almost absent


  1. Taiga- Northern Europe, Asia and North America. Moderate temperature than tundra. Also known as boreal forest.

The dominating vegetation is coniferous evergreen mostly spruce, with some pine and firs. The fauna consists of small seed eating birds, hawks, fur bearing carnivores, little mink, elks, puma, Siberian tiger, wolverine, wolves etc.


  1. Temperate Deciduous Forest- Extends over Central and Southern Europe, Eastern North America, Western China, Japan, New Zealand etc.

Moderate average temperature and abundant  rainfall. These are generally the  most  productive agricultural areas of the earth The flora includes trees like beech, oak, maple and cherry. Most animals are the familiar vertebrates and invertebrates.

  1. Tropical rain forest- Tropical areas  in  the equatorial regions, which is  a bound  with  life.  Temperature and rainfall high.

Tropical rainforest covers about 7% of the earth’s surface& 40% of the world’s plant and animal species.

Multiple storey of broad-leafed evergreen tree species are in abundance.

Most animals and epiphytic plants(An epiphyte is a plant that grows harmlessly upon another plant)  are concentrated in the canopy or tree top zones

  1. Savannah- Tropical region: Savannah is most extensive in Africa

Grasses with scattered trees and fire resisting thorny shrubs.

The fauna include a great diversity of grazers and browsers such as antelopes, buffaloes, zebras, elephants and rhinoceros;  the carnivores include lion, cheetah, hyena; and mongoose, and many rodents


  1. Grassland- North America, Ukraine, etc . Dominated by grasses. Temperate conditions with rather low rainfall. Grasses dominate the vegetation. The fauna include large herbivores like bison, antelope, cattle, rodents, prairie dog, wolves, and a rich and diverse array of ground nesting bird


  1. Desert- Continental interiors with very low and sporadic rainfall with low humidity. The days are very hot but nights are cold. The flora is drought resistance vegetation such as cactus, euphorbias, sagebrush. Fauna : Reptiles, Mammals and birds.

Aquatic Zones

Aquatic systems are not called biomes,

The major differences between the various aquatic zones are due to salinity, levels  of dissolved nutrients; water temperature, depth of sunlight penetration.


  1. Fresh Water Ecosystem-Fresh water ecosystem are classified as lotic

(moving water) or lentic (still or stagnant water).


  1. Marine Ecosystem-
  2. Estuaries-Coastal bays, river mouths and tidal marshes  form  the

estuaries.  In estuaries, fresh water from rivers meet ocean water and the two are mixed by action of tides.

Estuaries are highly productive as compared to the adjacent river or sea



a part of the earth where life can exist.

represents a highly integrated and interacting zone comprising of atmosphere (air), hydrosphere (water) and lithosphere (land) Life in the biosphere is abundant between 200 metres (660 feet) below the surface of the ocean and about 6,000 metres (20,000 feet) above sea level. absent at extremes of the North and South poles. Living organisms are not uniformly distributed  throughout the biosphere



ENERGY FLOW- Energy is the basic force responsible for all metabolic activities. The flow of energy from producer to top consumers is called energy flow  which is unidirectional.

Energy flows through the trophic levels: from producers to subsequent trophic levels. There is a loss of some energy in the form of unusable heat at each trophic level.

The trophic level interaction involves three concepts namely :-

  1. Food Chain
  2. Food Web
  3. Ecological Pyramids
  4. FOOD CHAIN- A food chain starts with producers and ends with top carnivores. The sequence of eaten and being eaten, produces transfer of food energy and it is known as food chain.

Grazing food chain-The consumers which start the food chain, utilising the plant or plant part as their food, constitute the grazing food chain.

This food chain begins from green plants at the base and the primary consumer is herbivore

For example, In terestrial ecosystem, grass is eaten up by caterpillar, which is eaten by lizard and lizard is eaten by snake.

In Aquatic ecosystem phytoplanktons (primary producers) is eaten by zoo planktons which is eaten by fishes and fishes are eaten by pelicans

Detritus food chain- The food chain starts from dead organic matter of decaying animals and plant bodies to the micro-organisms and then to detritus feeding organism called detrivores or decomposer and to other predators.


Litter —■Earthworms —■Chicken—■Hawk

Detritus food chain

The distinction between these two food chains is the source of energy for the first level consumers.


“A food web illustrates, all possible transfers of energy and nutrients among the organisms in an ecosystem, whereas a food chain traces only one pathway of the food”.


The steps of trophic levels expressed in a diagrammatic way are referred as

ecological pyramids.


The food producer forms the base of the pyramid and the top carnivore forms the tip. Other consumer trophic levels are in between.

The pyramid consists of a number of horizontal bars depicting specific trophic levels which are arranged sequentially from primary producer level through herbivore, carnivore onwards.  The length of each bar represents the total number of individuals at each trophic level in an ecosystem.

The ecological pyramids are of three categories-

1.Pyramid of numbers,

2.Pyramid of biomass, and

3.Pyramid of energy or productivity

  1. Pyramid of Numbers

This deals with the relationship between the numbers of primary producers and consumers of different levels. Depending upon the size and biomass, the pyramid of numbers may not always be upright, and may even be completely inverted.

(a) Pyramid of numbers – upright

In this pyramid, the number of individuals is decreased from lower level to higher trophic level.

This type of pyramid can be seen in grassland ecosystem.

(b) Pyramid of numbers – inverted

In this pyramid, the number of individuals is increased from lower level to higher trophic level.

A count in a forest would have a small number of     large producers, for e.g. few number of big trees.   This is because the tree (primary producer) being

few in number and would represent the base of the pyramid and the dependent herbivores  (Example – Birds) in the next higher trophic level and it is followed by parasites in the next trophic level. Hyper parasites being at higher trophic level represents higher in number.

A pyramid of numbers does not take into account the fact that the size of organisms being counted in each trophic level can vary

the pyramid of number does not completely define the trophic structure for an ecosystem.

  1. Pyramid of Biomass

In this approach individuals in each trophic level are weighed instead of being counted. This gives us a pyramid of biomass, i.e., the total dry weight of all organisms at each trophic level at a particular time.

Biomass is measured in g/m2.


(a) Upward -pyramid For most ecosystems on land, the pyramid of biomass has a large base of primary producers with a smaller trophic level perched on top


(b) Inverted pyramid-In contrast, in many aquatic ecosystems, the pyramid of biomass may assume an inverted form

  1. Pyramid of Energy

To compare the functional roles of the trophic levels in an ecosystem, an energy pyramid is most suitable.

An energy pyramid, reflects the laws of thermodynamics, with conversion of solar energy to chemical energy and heat energy at each trophic level and with loss of energy being depicted at each  transfer to another trophic level.

Hence the pyramid is always upward, with a large energy base at the bottom.


Movement of these pollutants involves two main processes:


  1. Bioaccumulation

refers to how pollutants enter a food chain. there is an increase in concentration of a pollutant from the environment to the first organism in a food chain.


  1. Biomagnification

refers to the tendency of pollutants to concentrate as they move from one trophic level to the next.  there is an increase in concentration of a pollutant from one link in a food chain to another.

In order for biomagnification to occur, the pollutant must be: long-lived, mobile, soluble in fats, biologically active.

If a pollutant is not active biologically, it may biomagnify, but we really don’t worry about it much, since it probably won’t cause any problems Examples : DDT.


The interaction between the organisms is fundamental for its survival and functioning of ecosystem as a whole.

Type of Biotic Interaction

  1. Mutualism:

both species benefit.

Example: in pollination mutualisms, the pollinator gets food (pollen, nectar), and the plant has its pollen transferred to other flowers for cross-fertilization (reproduction).


  1. Commensalism:

one species benefits, the other is unaffected.

Example: cow dung provides food and shelter to dung beetles. The beetles have no effect on the cows.


  1. Competition:

both species are harmed by the interaction.

Example: if two species eat the same food, and there isn’t enough for both, both may have access to less food than they would if alone. They both suffer a shortage of food


  1. Predation and parasitism:

one species benefits, the other is harmed.

Example : predation—one fish kills and eats ..parasitism: tick gains benefit by sucking blood; host is harmed by losing blood.


  1. Amensalism :

One species is harmed, the other is unaffected.

Example: A large tree shades a small plant, retarding the growth of the small plant. The small plant has no effect on the large tree.


  1. Neutralism :

There is no net benefit or harm to either species. Perhaps in some interspecific interactions, the costs and benefits experienced by each partner are exactly the same so that they sum to zero




The elements or mineral nutrients are always in circulation moving from non-living to living and then back to the non-living components of the ecosystem in a more or less circular fashion. This circular fashion is known as biogeochemical cycling (bio for living; geo for atmosphere).

  1. Nutrient Cycling:

The nutrient cycle is a concept that describes how nutrients move from the physical environment to the living organisms, and subsequently recycled back to the physical environment.

It is essential for life and it is the vital function of the ecology of any region. In any particular environment, to maintain its organism in a sustained manner, the nutrient cycle must be kept balanced and stable.


Types of Nutrient Cycle

Based on the replacement period a nutrient cycle is referred to as Perfect or Imperfect cycle.

A perfect nutrient cycle is one in which nutrients are replaced as fast as they are utilised.

Most gaseous cycles are generally considered as perfect cycles.

In contrast sedimentary cycles are considered relatively imperfect, as some nutrients are lost from the cycle and get locked into sediments and so become unavailable for immediate cycling.

Based on the nature of the reservoir, there are two types of cycles namely Gaseous and sedimentary cycle

Gaseous Cycle — where the reservoir is the atmosphere or the hydrosphere, and

Sedimentary Cycle — where the reservoir is the earth’s crust.


  1. Gaseous Cycles:

Water Cycle (Hydrologic)

The hydrologic cycle is the continuous circulation of water in the Earth-atmosphere system which is driven by solar energy.

Water moves from one reservoir to another by the processes of evaporation,

transpiration, condensation, precipitation, deposition, runoff,

infiltration, and groundwater flow.


  1. The Carbon Cycle

without carbon dioxide life could not exist, because it is vital for the production of carbohydrates through photosynthesis by plants. It is the element that anchors allorganic substances from coal and oil to DNA(deoxyribonudeic acid: the compound that caries genetic information) Carbon cycle involves a continuous exchange of carbon between the atmosphere and organisms. Carbon from the atmosphere moves to green plants by the process   of photosynthesis, and then to animals. By process of respiration and decomposition of dead organic matter it returns back to atmosphere.


  1. The Nitrogen Cycle

an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins.

There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms needs to be ‘fixed’, that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants. on earth it is accomplished in three different ways:

(i) By microorganisms (bacteria and blue-green algae)


(ii) By man using industrial processes (fertilizerfactories) and

(iii) To a limited extent by atmospheric phenomenon such as thunder and lighting

The amount of Nitrogen fixed by man through industrial process has far

exceeded the amount fixed by the Natural Cycle.

As a result Nitrogen has become a pollutant which can disrupt the balance of

nitrogen. It may lead to Acid rain, Eutrophication and Harmful Algal Blooms.

Certain microorganisms are capable of fixing atmospheric nitrogen into

ammonium ions. These include free living nitrifying bacteria (e.g. aerobic

Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in  association with leguminous plants(pulse etc) and symbiotic bacteria    living in non leguminous root nodule plants (e.g. Rhizobium) as well as blue green algae (e.g. Anabaena, Spirulina).

Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialised bacteria:

Nitrosamines bacteria promote transformation of ammonia into nitrite. Nitrite isthen further transformed into nitrate by the bacteria Nitrobacter.

The nitrates synthesised by bacteria in the soil are taken up by plants and converted into amino acids, which are the building blocks of proteins.

These then go through higher trophic levels of the ecosystem.

During excretion and upon the death of all organisms nitrogen is returned to the soil in the form of ammonia.

Certain quantity of soil nitrates, being highly soluble in water, is lost to the system by being transported away by surface run-off or ground water. In the soil as well as oceans there are special denitrifying bacteria (e.g. Pseudomonas), which convert the nitrates/nitrites to elemental nitrogen. This nitrogen escapes into the atmosphere, thus  completing the cycle.

The periodic thunderstorms convert the gaseous nitrogen in the atmosphere to ammonia and nitrates which eventually reach the earth’s surface through precipitation and then into the soil to be utilized by plants.(Better if You Check Diagram)

  1. Sedimentary Cycle

Phosphorus, calcium and magnesium circulate by means of the sedimentary cycle.

(a) Phosphorus Cycle

Phosphorus plays a central role in aquatic ecosystems and water quality.

Phosphorus occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion and minning activities.

This is the nutrient considered to be the main cause of excessive growth of rooted and free-floating microscopic plants in lakes.

The main storage for phosphorus is in the earth’s crust.

On land phosphorus is usually found in the form of phosphates.

By the process of weathering and erosion phosphates enter rivers and streams that transport them to the ocean.

In the ocean once the phosphorus accumulates on continental shelves in the form of insoluble deposits

After millions of years, the crustal plates rise from the sea floor and expose the phosphates on land.

After more time, weathering will release them from rock and the cycle’s

geochemical phase begins again.

(b) Sulphur Cycle

The sulphur reservoir is in the soil and sediments where it is locked in organic

(coal, oil and peat) and inorganic deposits (pyrite rock and sulphur rock) in the

form of sulphates, sulphides and organic sulphur.


It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution.

The sulphur cycle is mostly sedimentary except two of its compounds hydrogen sulphide

(H2S) and sulphur dioxide (SO2) add a gaseous component to its normal sedimentary cycle.

Atmospheric sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak sulphuric acid.

sulphur in the form of sulphates is take up by plants and incorporate through a series of metabolic processes into sulphur bearing amino acid which is incorporated in the  proteins of autotroph tissues. It then passes through the grazing food chain.

Sulphur bound in living organism is carried back to the soil, to the bottom of ponds and lakes and seas through excretion and decomposition of dead organic material.



a universal process of directional change in vegetation, on an ecological time scale. occurs when a series of communities replace one another due to large scale destruction either natural or manmade.

continously -one community replacing another community, until a stable, mature community develops.

The first plant to colonise an area is called the pioneer community. The final stage of succession iscalled the climax community.

The stage leading to the climax community are called successional stages

or seres. characterised by the following: increased productivity, the shift of nutrients from’ the reservoirs, increased diversity of organisms with increased niche development, and a gradual increase in the complexity of food webs.

Primary Succession

In primary succession on a terrestrial site the new site is first colonized by a few hardy pioneer species that are often microbes, lichens and mosses.

The pioneers through their death any decay leave patches of organic matter in which small animals can live.

The organic matter produced by these pioneer species produce organic adds during decomposition that dissolve and etch the substratum releasing nutrients to the substratum. Organic debris accumulates in pockets and crevices, providing soil  in which seeds can become lodged and grow.

As the community of organisms continues to develop, it becomes more diverse and competition increases, but at the same time new niche opportunities develops.

The pioneer species disappear as the habitat conditions change and invasion of new species progresses, leading to the replacement of the preceding community.

Secondary Succession

Secondary Succession occurs when plants recognize an area in which the climax community has been disturbed.

Secondary Succession  is the sequential development of biotic communities after the complete or partial destruction of the existing community.

This abandoned farmland is first invaded by hardy species of grasses that can survive in bare, sun-baked soil. These grasses may be soon joined by tall grasses and herbaceous plants.

These dominate the ecosystem for some years along with mice, rabbits, insects and seed- eating birds.


Eventually, some trees come up in this area, seeds of which may be brought by wind or animals. And over the years, a forest community develops. Thus an abandoned farmland over a period becomes dominated by trees and is transformed into a forest.

The differences between primary and secondary succession, the secondary succession starts on a well-developed soil already formed at the site. Thus secondary succession is relatively faster as compared to primary succession which may often require hundreds of years.

Autogenic and Allogenic Succession

When succession is brought about by living inhabitants of that community itself, the process is called autogenic succession, while change brought about by outside forces is known as allogenic succession.

Autotrophic and Heterotrophic succession

Succession in which, initially the green plants are much greater in quantity is known as autotrophic succession;  and the ones in which the heterotrophs are greater in quantity is known as heterotrophic succession.

Succession would occur faster in area existing in the middle of the large continent. This is because, here all prop gules or seeds of plants belonging to the different seres would reach much faster, establish and ultimately result in climax community.


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