Ecosystem = Ecological System

(Eco = Environment; System = Interacting & interdependent complex)

  • ‘Ecosystem’ term was first used by A.G. Tansley (1935), describing a natural unit consisting of both living & non- living parts, which interact, forming a stable system.
  • Fundamental concepts of ecosystem include…
    • Energy flow through food chains or food webs.
    • Nutrient cycling biogeochemically.

Ecosystem definition:

            An ecological unit which includes all organisms (biotic community) in a given area, interacting with their physical environment, in a self-sufficient manner, leading to formation of proper biotic structures & cycling of material among living & non-living components.

As indicated in the definition above by the term ‘self-sufficient’, ecosystem is the first unit of ecological hierarchy which is complete, as it carry all the biological and physical components necessary for survival. It is a functional unit having capability of transformation, storage & circulation of energy.

  • The term ‘biogeocoenosis’ in Russian & central European literature is same concept as Ecosystem.
    • Biogeocoenosis = Biocoenosis + its habitat ‘ecotope’
    • Biocoenosis: Bio = living; conenose = collection of life forms found together, interacting, in an ecosystem.
    • Biocoenosis comprises phytocoenosis, zoocoenosis, microcoenosis & is considered equivalent to biotic community.
  • Ecosystem principles can be applied at all levels, for example, right from pond, lake, desert etc. till whole planet or even beyond.
  • One thing to keep clear in mind is that an ecosystem is more than an ecoregion.

(Ecoregion = ecological region, which is ecologically & geographically defined, characterized by specific ecological patterns, flora, fauna, soil, climate etc.)

Instead Ecosystem is a functional unit with inputs & outputs & the boundaries are either natural or arbitrary.

Graphic Model for an Ecosystem

It consists of…

  • A box labelled as system, representing area of interest. Boundary of the system can be arbitrary or natural, for example, a block of forest, shore of a lake, a whole pond etc.
  • Two large funnels- labelled one as ‘Input environment’ & other as ‘Output environment’.
Ecosystem Model

There are interactions between three basic components –

  1. Community
  2. Energy flow
  3. Material cycling

Energy Flow:

  • Energy is a necessary input.
  • Energy flow is one way.
  • Sun – ultimate energy source, directly supports most natural ecosystems.
  • Other energy sources- wind, water, fossil fuel etc.
  • By community,some of the incoming solar energy is transformed into organic matter- a higher quality energy form.
  • But most input energy is degraded, flows out of system in form of heat i.e. heat sink.
  • Energy can be…
    • Stored
    • Exported
  • Energy can never be reused.

Material Cycling:

  • Water, air, nutrients etc. essential for life constantly enter & leave ecosystem
  • In same way, Organisms & their reproductive stages enter (Immigrate) & leave (Emigrate) the system.
  • Additionally, some non- essential material also enter & leave.
  • Nutrients like carbon, nitrogen, phosphorus etc. & water can be reused.
  • Efficiency of recycling + import & export of nutrients vary from ecosystem to ecosystem.

Formula of conceptually complete ecosystem:

            “Ecosystem = IE + S + OE”


  • IE = Input Environment
  • S = System (Delimited)
  • OE­ = Output Environment

This solves the problem – where to draw lines around an entity.


  • It doesn’t matter how a system is delimited & in how much portion.
  • The extent to which input & output environment varies, depends upon…
    • Size of system: the larger the system, the less dependent it is on externals i.e. input & output.
    • Intensity/Rate of metabolism: the higher the metabolic rate of the system, the greater is the input & output.
    • Balance between Autotrophs & Heterotrophs: the less the balance, more the externals i.e. input & output required to balance.
    • Development stage of the system: Young & mature system differ in input & output requirement. (Refer- Ecological Succession)

Example: A large forest has less input & output requirement than a lake or a pond.

Harjeet Kaur

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