Ecosystem- Definition, Structure, Factors, Types, Functions

The ecosystem is the basic unit of our environment and comprises living organisms and non-living and how they interact with each other.

In simple words, a geographical area where plants, animals, and other organisms, as well as weather and landscape, coexist to form a life bubble is called an ecosystem or ecological system. The respective study is called ecology.


The term ecosystem was first used by Arthur Tansley (a British ecologist) in which one of his publications in 1935, whereas the term was actually coined by A.R. Clapham at the request of Tansley. At first, Tansley included only organisms but later on the environment as well. 

Further other scientists also contributed and explored this field; some of them are G.E. Hutchinson, H.T. Odum, and E.P. Odum, among many others.

The ecosystem study is based on these four main factors:

I. Abiotic (Non-living things)

II. Biotic (Living Beings)

III. The mutual interaction between biotic and abiotic

IV. The space they occupy

Basic Components of Ecosystem
Figure: Basic Components of Ecosystem.

Structure of Ecosystem

It includes the substances or things that make the ecosystem. It consists of two types of components:

1. Biotic Components

These are the living elements of the ecosystem. They can be subdivided into three main types.

Autotrophs (auto=self; troph=nutrition/nourishment)

They are the organisms that prepare their own food. They can also be called producers. They are the first line in the food chain.

a. Photoautotrophs (Photo=light): The autotrophs that prepare their food by using sunlight are called photoautotrophs. They do so via photosynthesis in the presence of sunlight, water, and carbon dioxide. For eg, Green plants, Bacteria (Cyanobacteria), algae, etc.

Note: Photoautotrophs are often confused with photoheterotrophs which, although use light, but instead Carbon dioxide, they use other organic materials as sources of carbon and cannot prepare their own food.

b. Chemoautotrophs (Chemo=chemicals): They are generally bacteria that synthesize some chemical components to produce their own food. For eg., nitrogen-fixing bacteria, iron-oxidizing bacteria, etc.


They are those organisms that cannot synthesize food on their own and just use the producers or other organisms as food. They can be primary (feeding on producers directly), secondary (feeding on primary consumers), and so on.

a. Herbivore (Herb=plants; vore=kind of diet): They only consume grass or plants as a food source. For e.g. Cows, Buffalo, deer, goats, etc.

b. Carnivore (Carni=meat): They solely depend on other animals’ flesh for their food. For e.g., Lion, Tiger, etc.

c. Omnivore (Omni=everything): As the name suggests, they can consume anything no matter it is plant or animal meat. For e.g. Cats, Dogs, Humans, etc.


These include those organisms that feed on dead and decayed organic matter. For e.g. microbes such as bacteria and fungi.

2. Abiotic Components

These are the non-living components of the ecosystem.

Physical factors: These comprise the sunlight, temperature, humidity, etc.

Chemical factors: These comprise the chemicals such as air and water components.

Functions of the Ecosystem

It depicts the ways of interaction of the abiotic and biotic components. The main components of the function are: 

a. Physical (Energy Flow)

The energy which follows in the ecosystem is always fixed in one direction or unidirectional. 

  • It always flows from producers to consumers (herbivores to carnivores) and cannot be vice-versa.
  • The energy at each stage of transfer is lost in some amount. So if the energy produced received by plants from sunlight is 100%, then they receive only a few amounts of it. After consuming plants, the animals will receive maybe only 10% of the total energy, not exactly all energy. 
  • The energy is lost during respiration, growth, movement, and other activities. 
  • This is why trophic levels can be up to four or five as the energy becomes minimal at lower trophic levels, and the organism cannot survive with that amount.
  • Different energy flow models depict the transfer of energy, such as the universal energy flow model, single channel energy flow model, and double channel energy flow model.

b. Biological (Food, chain, Food web, and Ecological Pyramids)

Food Chain

It is a sequence or order in which one organism feeds on another. Every organism on this earth is interconnected through the food chain i.e. each organism depends on others for its food requirements. The main definition of the food chain is “it is the sequence of eating and being eaten with the transfer of energy in every stage.” It represents the diet or feeding behavior of organisms along with the flow of energy in the ecosystem. An example of a food chain is the grass that depends on sunlight and oxygen for food which is consumed by grasshopper feeding on grass, which gets eaten by frogs and the frogs are taken as a diet by snakes which are eaten by an eagle and as eagles die they are buried in the soil and decomposed by decomposers which become minerals for plants to grow again.

Grass       Grasshopper       Frogs       Eagle       Dies and gets decomposed by decomposers       Decomposed matters utilized by grass (Cycle continues).

The food chain can also be ordered at the trophic level. The energy moves from one trophic level to another.

1. First Trophic Level: It includes producers which form the energy, such as green leafy plants.

2. Second Trophic Level: The one which feeds directly on producers for energy comes in this level. Such as the grasshopper in the above example.

3. Third Trophic Level: The one which feeds on organisms of the second trophic level comes under this. For e.g. Frogs and Eagles.

The food chain is of two types:

  1. Grazing Food Chain: It is the one that starts from sunlight. The energy from sunlight is transferred to the producers and then to the consumers, to the decomposers, and again to the producers.
  2. Detritus Food Chain: It is the one that begins from dead organic matter. For instance, dead leaves are eaten by insects which are further consumed by birds and so on.

Food Web

It is actually the interconnection or network between different food chains. It is an intricate representation of different food chains that are interrelated. For e.g. grass can be eaten by grasshoppers and goats; grasshoppers can be eaten by frogs, and frogs as well goats can be eaten by one or more carnivores which can be interrelated on the basis of feeding.

Importance of the food chain and food web:

  • Ecological Balance: It helps to predict the reason for the imbalance or ecological disturbance in the ecosystem.
  • Biomagnification: It is the process by which chemicals increase in concentration at different trophic levels. It takes place through the food chain and can be predicted by it. For, eg., the reason for the decrease in the number of vultures was predicted to be the consumption of dead bodies of cattle which were injected with efficient chemicals to boost their working stamina which then entered vultures and they started to die.

Ecological Pyramids

They are the representations of the number, biomass, and amount of energy at various trophic levels of the food chain in the form of graphs or pyramids. The producers are kept at the bottom of pyramids, and the consumers above, respectively, are based on their food chain. They can be of different types and can be inverted or upright based on the type of ecosystem. 

  • Pyramid of Numbers: It depicts the number of organisms at different trophic levels. E.g., In an aquatic ecosystem, the number of plankton is numerous, and they are kept at the bottom of the pyramid with broad bottoms, and the insects consuming that plankton are lesser in number; the small fishes eating insects are lesser than insects, and the large fishes are minimal in number that consume on those fishes, so they are kept at the top with a narrow top. So the pyramid of the number of aquatic ecosystems is upright.
  • Pyramid of Biomass: It represents the dry weight of different organisms involved in a food chain. For e.g. In an aquatic ecosystem, the dry mass of phytoplanktons is lesser than those of small fishes, and the large fishes have a large dry mass. Hence the pyramid formed is inverted.
  • Pyramid of Energy: It represents the amount of energy at different levels of the food chain. As energy flow is unidirectional and decreases at each step from producer to consumer, so the pyramid of energy is always upright.

c. Biogeochemical cycle (Nutrient cycling)

The biogeochemical cycle is the phenomenon by which nutrients like carbon, nitrogen, phosphorus, etc., are available from the atmosphere or surrounding to the plants and then to the consumers in different forms such as carbohydrates, proteins, phosphates, etc., and get back to the atmosphere in their original form. It is the transfer of nutrients from abiotic to biotic components and vice-versa. The biogeochemical cycle is multi-directional in contrast to the energy flow, which is uni-directional. It includes the water cycle, carbon cycle, nitrogen cycle, etc.

Types of Ecosystem

Based on the location, the ecosystem can be divided into two types: 

Terrestrial Ecosystem

It includes the ecosystem present on the land. It can be further divided into: 

  • Forest Ecosystem: These areas on land receive a very large amount of rainfall, which is the reason for the diverse types of large trees and animals. Based on their distance from the equator, forests can be of two types:
    • Tropical Forest: The forests close to the equator are called tropical. It includes tropical rainforest, tropical deciduous, and tropical scrub forest.
    • Temperate Forest: The forests that are far from the equator are called temperate forests. It includes temperate rainforest, temperate deciduous, and coniferous forest.
  • Grassland Ecosystem: If the terrestrial ecosystem receives a moderate amount of rainfall that can be enough for the growth of grasses, then it is called a grassland ecosystem. They can be of three types that include tropical grassland (e.g. Savanna Grassland), temperate grassland (e.g. Pampas), and polar grassland.
  • Desert Ecosystem: If the terrestrial ecosystem receives a very low amount of rainfall, then it is called a desert ecosystem. The components of this ecosystem are adaptive to survive in those conditions. For eg., Camels have special pouches where they store water for later consumption. Thorny plants such as cacti are present in this ecosystem. They are two types:
    • Hot Desert: The temperature is extremely high in this kind of desert. It includes the tropical desert (Sahara), and temperate desert (Mojave Desert).
    • Cold Desert: The temperature is relatively low in these deserts. One example is the Gobi Desert.

Aquatic Ecosystem

It includes the ecosystem present in water. The food chain of the aquatic ecosystem comprises plants or phytoplankton, insects, small fishes, large fishes, turtles, and other large aquatic animals. It is further divided into two types based on the amount of salt content in the water:

Freshwater Ecosystem

The salt content is very low in comparison to the saltwater ecosystem. It can be subdivided into two types: 

Lentic water: Water is stationary. For eg. pond ecosystems and lake ecosystems. Based on the availability of sunlight, the pond ecosystem can be divided into different zones:

  • Littoral Zone: Plenty amount of sunlight is available in this zone. It is the top layer of water, and generally, the plants survive in this zone.
  • Limnetic Zone: Moderate amount of sunlight is available in this zone. It is the middle layer of water. The food chain can operate quite efficiently in this zone.
  • Profundal Zone: It includes the deep layer of water that receives minimal or no sunlight where decomposers, such as bacteria, fungi, etc., survive.

Lotic water: Water is always moving or flowing. For, eg. the river ecosystem. It generally originates from mountains, and the respective layer has a high amount of dissolved oxygen. The middle layer has a lesser amount of dissolved oxygen and is warm. This layer flows through a long distance and collects a lot of pollutants. The last segment is called the delta, which finally leads to the deposition of water in oceans.

Saltwater Ecosystem

It has a very large amount of salt content. For eg. Seas and oceans. Its larger size and connections with different landmasses, as well as freshwater ecosystems such as rivers, are the reason for its wide range of biodiversity. On the basis of the availability of light, it can be divided into the euphotic zone (a large amount of sunlight), an aphotic zone (less amount of light), and an abyssal plain (totally dark).

It also includes estuaries where the river water meets the ocean water, and there is a higher fluctuation of nutrients and temperature.

Ecological Succession

It is the process by which the species that are present in an ecosystem change or vary over time due to the changing environment. This is to say that if any area becomes devoid of living beings after natural calamities, the organisms either migrate to those places later on or the organisms evolve by adapting themselves to the respective environment hence one species can be replaced by other gradually. It is of two types:

  • Primary Succession: The soil is unavailable at first in this type. The organisms such as lichen act on the rocks and break them down to form soil, or soil formation can also occur by the phenomenon such as weathering. After that, many species can immigrate or grow over that area forming a climax community.
  • Secondary Succession: This succession occurs rapidly as the soil is already formed and different species already have a suitable environment to grow and survive in those areas, eventually forming a climax community.


  1. P. A. Matson, Peter Morrison Vitousek, Melissa C. Chapin (2nd ed.). New York: Springer. ISBN 978-1-4419-9504-9.
  2. Willis, A.J. (1997) “The Ecosystem: An Evolving Concept Viewed Historically”. Functional Ecology. 11(2): 268-271
  3. Accessed from:; Accessed on: 11/15/2022
  4. Chapin F. S. Matson P. A. Vitousek P. M. & Chapin M. C. (2011). Principles of terrestrial ecosystem ecology (2nd ed.). Springer.
  5. Balasubramanian A. (2008) Ecosystem and its components. University of Mysore.

About Author

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Bikash Dwivedi

Bikash Kumar Dwivedi completed his undergraduate degree (B.Sc.) in Microbiology from St. Xavier's College, Kathmandu, Nepal. He works in molecular biology and medical microbiology for the betterment of mankind. He is interested in the field of antibiotic resistance, immunology, and disease epidemiology.

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