Introduction
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’.
There are interactions between three basic components –
- Community
- Energy flow
- 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”
Where,
- IE = Input Environment
- S = System (Delimited)
- OE = Output Environment
This solves the problem – where to draw lines around an entity.
Since,
- 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.
