Energy flow in an ecosystem

Energy flow can be defined as the process or phenomena of transfer of energy from one component of ecosystem to another component.

Common pathway for energy transfer in biological system is as follows:

Ecosystem components consist of primary producers, decomposers and detritivores, a pool of dead organic matter, herbivores, carnivores and parasites. They serve both as source of energy and matter.

Energy flow takes place through food chain, food web and biogeochemical cycles.

MODELS OF ENERGY TRANSFER:

There are two important models for energy transfer in ecosystem;

1.Unidirectional energy flow model.

2. Y-Shaped model

Unidirectional energy flow model

                                                           Y-Shaped model

1.Grazing Food Chain: It starts with green plants(Producers) then goes to grazing herbivores then carnivores. In this food chain one animal captures other.

2.Detritous Food Chain: It starts with dead organic matter then goes up to detrivores.

Trophic relationships- Food Chain and Food Web

In a trophic relationship one organism consumes organic molecules from another organism (or a decomposer consumes organic molecules from dead organic matter).

A food chain shows a simple sequence of trophic relationships (e.g. producer → primary consumer → secondary consumer).

A food web shows the multiple complex trophic relationships among organisms in an ecosystem.

Dead organic matter includes dead leaf, litter, dead plants, fallen leaves etc.

Thermodynamics and Energy Flow

First Law: “Energy can neither be created nor destroyed. It can only be converted from one form to another”

The energy of sun that is radiation energy get converted to chemical energy by plants. So energy is not created but converted between different forms.

Second Law: “Heat does not flow from a colder object to a hotter object except by the application of energy”.

Large part of energy get lost in form of heat (Respiration)

Other way of explaining the the energy flow in ecosystem is using concept of Biomass.

Biomass means the mass of organisms per unit area of ground. It is expressed in units of energy (J m−2 ) or dry organic matter.

The primary productivity of a community is the rate at which biomass is produced per unit area by plants, the primary producers by trapping the energy from sun. It can be expressed either in units of energy (e.g. J m−2 day−1 ) or dry organic matter (kg ha−1 year−1 ) or carbon (g C m−2 year−1 )

The total fixation of energy by photosynthesis is referred to as gross primary productivity (GPP).

A portion of this is respired away by the plants (autotrophs) and is lost from the community as respiratory heat (RA – autotrophic respiration).

The difference between GPP and RA is known as net primary productivity (NPP) and it represents the actual rate of production of new biomass that is available for consumption by heterotrophic organisms (bacteria, fungi and animals).

The rate of production of biomass by heterotrophs is called secondary productivity

NPP= Net Primary Productivity

DOM=Dead Organic Matter

R= Respiration