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An ecosystem is a population of living organisms of plants, animals and microbes in association with the nonliving entities of their environment. The living organisms like the plants, animals and microbes make up the biotic component of the ecosystem and the nonliving components like the air, water and mineral soil make up the abiotic components of the ecosystem. The biotic and the abiotic components of the ecosystem ate linked together through nutrient cycles and energy flows.

Ecosystems are characterized by the interactions among the organisms and between the organisms and their environment. The flow of energy through the ecosystem is primarily obtained from the sun. This energy enters the ecosystem through the process of photosynthesis. Animals that feed on plants make this matter and energy and move to the higher levels of the ecosystem. Decomposers breakdown dead organic matter and release carbon back to the atmosphere and facilitate nutrient cycling.   

The study of ecosystems consists of the study of certain processes that link the biotic and the abiotic components. Ecosystems are controlled by external and internal factors. External factors like climate, soil and topography control the overall existence of the ecosystem. 


Ecosystem Definition

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Ecosystem is defined as a structural and functional unit of biosphere or part of the nature that consists of the living and the nonliving communities that interact and exchange materials between them. The ecosystem consists of the biological or biotic or living community that occurs in the physical and chemical factors that make up the nonliving or abiotic component. There are many examples of ecosystem like a pond, forest, estuary and grassland. 

Ecosystem Structure

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The structure of an ecosystem is obtained by the systematic organization of the biotic and abiotic components of that particular ecosystem. The structure of the ecosystem means the composition of the biological community that includes distribution, number, biomass, etc. It also includes the distribution and quantity of non-living materials and the gradient of conditions of existence. 

The structure of ecosystem has two main components the abiotic and the biotic components. 

Abiotic Components
  • Abiotic components consist of the non-living components in the ecosystem.
  • The abiotic components have a strong influence on the structure, distribution and behavior and the relationship of organisms. 
  • Abiotic components are of two types mainly - Climatic factors and the Edaphic factors. 
  • Climatic factors include rain, temperature, light, humidity, wind, pH, minerals, inorganic components, etc. 
  • Edaphic factors include the pH, organic and inorganic components, minerals, etc. 
Biotic Components
  • Biotic components of an ecosystem include the living organisms - plants animals and microorganisms.
  • Based on their role in the ecosystem the biotic component of an ecosystem can be classified into three main groups - Producers, Consumers, Decomposers or Reducers. 
  • Producers are the autotrophic plants that produce their own food. 
  • Consumers are the animals that are unable to synthesize their own food and depend on producers for their food. 
  • Decomposers are the microorganisms like the bacteria and fungi that breakdown the dead organic materials of producers and consumers.

Types of Ecosystem

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Ecosystem can be many types. It may be natural like forest, lake, oceans, seas, etc; or man-made like aquarium, zoo, crop field etc; temporary like rain-fed pond and streams or permanent like a lake or forest, aquatic ecosystem like ponds, rivers, seas, oceans or terrestrial like grassland, forests, etc. Ecosystem may be small as a drop of pond water or large as an ocean. Ecosystems are self-regulating and self-sustaining units. 

Components of an Ecosystem

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Ecosystem consists of two basic components 
(i) Abiotic components and
(ii) Bitotic components

Abiotic Components 

The abiotic components consists of the non-living, physico-chemical factors such as the basic components of the atmosphere and air, water and soil. Abiotic factors are classified into three categories: Climatic factors, Edaphic factors and Inorganic substances.
  • Climatic factors comprises of the climatic system and physical factors of the environment like humidity, light, temperature, wind, etc. 
  • Edaphic factors are describe the structure and composition of the soil; including the physico-chemical properties of the soil. 
  • Components like water, carbon, sulphur, nitrogen, phosphorus and so on comprise the inorganic part of the ecosystem. 

Biotic Components

Biotic components of an ecosystem comprises of the living part which includes a number of interrelated populations belonging to different species in a common environment. Biotic community is categorized into autotrophs, heterotrophs and saprotrophs.

Autotrophs or Producers
  • Autotrophs are self feeders, i.e., they prepare their own food. They are also known as producers.
  • They are photosynthetic plants have chlorophyll which synthesize food in the form of high energy compounds from inorganic raw materials with the help of sunlight, this process is known as photosynthesis. 
  • Autotrophs forms the basis of the biotic system. In terrestrial ecosystem the autotrophs are mainly rooted plants. 
  • In aquatic ecosystems, floating plants called phtoplankton and shallow water rooted plants are the producers. 
Heterotrophs or Consumers
  • Heterotrophs are organisms that feed on autotrophs. 
  • Heterotrophs are called consumers which generally feed on other organisms. 
  • Consumers are mainly herbivores and carnivores.
  • Herbivores are referred to as first order consumers and they directly feed on plants. Example: Cattle, deer, rabbit, etc. 
  • Consumers in the acquatic ecosystem are protozoans, crustaceans, etc. 
  • Carnivores are animals that feed or prey upon other animals. 
  • Primary carnivores are second order consumers which include animals which feed on the herbivores. Example: Frog, predatory birds, snakes,etc.
  • Secondary carnivores are referred to as third order consumers include animals that feed on the primary carnivores. Example: Wolf, peacock, owl, etc. 
  • Secondary carnivores are preyed upon by some larger carnivores, they are tertiary carnivores or quarternary consumers and include the animals that feed on secondary carnivores. Example: Lion, tiger, etc. 
  • The larger carnivores are not eaten by any other animals and are called to carnivores. 
Saprotrophs or Decomposers
  • Saprotrophs are also known as decomposers. 
  • The saprotrophs break down the complex organic compounds of dead matter of plants and animals. 
  • Decomposers absorb a part of decomposition products for their own nourishment and the remaining substances are added as minerals. These minerals are reused as nutrients by plants. 

Energy Flow

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  • Energy cannot be reused indefinitely though matter circulates.
  • Energy from the sun or the solar energy is converted by the photosynthetic producers into chemical energy in the form of carbohydrates in plants. 
  • Primary consumers like the herbivores consume the plant carbohydrates and so the chemical energy is transferred to them. 
  • Herbivores are consumed by carnivores, so the energy is further transferred into the next trophic level. 
  • In these animals the chemical energy is used as mechanical energy and heat. The chemical energy in the food molecules is stored as ATP molecules. This stored energy is used by the body cells for synthesis of new chemical compounds and for mechanical work. 
  • Energy used at each trophic level, only 10% of it is transferred to the next trophic level. 
  • At the last trophic level, that is with the decomposer no energy is left for recycling. 
  • Hence, energy flow from sun to the producers to consumers is in a single direction only. 

Biogeochemical Cycles

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  • Materials that are synthesized by the producers are eaten and assimilated by the consumers. 
  • Decomposers breakdown all the organic material in the bodies of consumers into inorganic material.
  • These inorganic substances are rebuilt into organic compounds by the synthetic activities of the consumers. Thus, matter circulates in nature. 
  • Though there is constant change in the form of matter, there is not overall loss or gain. 
  • The flow of nutrients between the non-living and the living organisms is a cycle and is known as biogeochemical cycle. 
  • Major nutrient elements like carbon, hydrogen, oxygen and nitrogen are circulated again and again between living and non-living components of the ecosystem.  

Ecosystem Function

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Ecosystem function is the biological, geochemical and physical processes and components that occur within an ecosystem. Functions of the ecosystem relate to the structural components of an ecosystem, how they interact with each other, within ecosystem and across ecosystem. Ecosystem functions are sometimes called ecological processes. 
  • The functional aspects of an ecosystem helps to keep the components of the ecosystem running together. 
  • Few important aspects of ecosystem are dependent on the biodiversity and maintenance of stability in the ecosystem. 
  • The numerical strength and biomass of organisms affect the functioning of the ecosystem. 
  • The biotic community in an ecosystem usually contain a few species represented by a large number of individuals or by a large biomass and a comparatively large number of species occurring in small numbers. 
  • Under the conditions of stress the number of indigenous species is usually reduced, only a few species may survive and the frequency of the occurrence of stress may be very high. 
  • Under extreme conditions of stress like in the arctic and the antarctic regions, the total number of species in an ecosystem is reduced. 
  • An ecosystem is considered to be stable if its structure and function remain more or less the same from year to year. 
  • A system with high species diversity and low dominance is less productive but stable. 
  • A system with a low species diversity and high dominance is more productive but unstable. 
In an ecosystem two processes proceed simultaneously:
  • Energy flow and 
  • Biogeochemical cycle
The energy flow is in a single direction and is non-cyclic, while the biogeochemical flow is cyclic. 
More topics in Ecosystem
Food Web Ecological Pyramid
Ecological Succession Biogeochemical Cycles
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