Ecosystem (Introduction)

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 –

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”

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.