Energy Flow

Except for the deep sea hydro-thermal ecosystem, sun is the only source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 percent of it is photosynthetically active radiation (PAR). We know that plants and photosynthetic bacteria (autotrophs), fix Sun's radiant energy to make food from simple inorganic materials. Plants capture only 2-10 percent of the PAR and this small amount of energy sustains the entire living world. So, it is very important to know how the solar energy captured by plants flows through different organisms of an ecosystem. All organisms are dependent for their food on producers, either directly or indirectly.

1.0Definition of Energy Flow

Energy flow in ecology refers to the transfer of energy through an ecosystem, starting from the input of sunlight and its conversion into chemical energy by primary producers, and then its passage through various trophic levels of consumers and decomposers. 

2.0Law of Thermodynamics

The storage, expenditure, transformation of energy is based on two basis law of thermodynamics : 

• First law of Thermodynamics :- Energy is neither created nor destroyed but only transformed from one state to another state.
• Second law of Thermodynamics (the law of entropy) :- The transfer of food energy from one to another organism leads to loss of energy as heat due to metabolic activity. Further, ecosystems are not exempt from the Second Law of thermodynamics. They need a constant supply of energy to synthesize the molecules they require, to counteract the universal tendency toward increasing disorderliness.

3.0Biotic components of Ecosystem

Primary Producers (Autotrophs): 

• Producers, the autotrophs of an ecosystem, include green plants that synthesize their own food through photosynthesis. This process involves the absorption of solar energy, converting it into chemical energy.Producers are often referred to as transducers or converters.
• Solar energy serves as the primary and ultimate source of energy in ecosystems, entering through the photosynthetic activities of producers. In aquatic ecosystems, phytoplankton, floating plants, are major autotrophs, contributing significantly to energy capture.

Consumers

All the heterotrophs of the ecosystem are known as consumers. They directly (herbivores) or indirectly (Carnivores) depend on the producers for food.

Types of Consumers

Consumers are of two types: macro consumers and micro consumers. 

(i) Macro Consumers : Macro consumers engage in internal digestion, beginning with the ingestion of food. They are further classified into specific types:

• Primary Consumers: These organisms directly acquire food from producers or plants, acting as herbivores in the ecosystem. Examples include cows, grazing cattle, and rabbits. Interestingly, they are also recognized as secondary producers, highlighting their crucial role in energy transfer.
• Secondary Consumers or Primary Carnivores: This category comprises animals that feed on primary consumers, preying on herbivores. Examples encompass dogs, cats, and snakes, emphasizing their role in maintaining ecological balance.
• Top Consumers: These animals play a pivotal role in the food chain by hunting and consuming other animals. Notably, they are not typically subjected to predation in their natural environment, contributing to the regulation of the ecosystem.

(ii) Micro Consumers Or Decomposers : 

• Micro consumers or decomposers, also known as saprotrophs or osmotrophs, play a crucial role in ecosystems by breaking down the remains of producers and consumers. Bacteria and fungi are the primary decomposers, releasing enzymes externally to decompose dead organic matter into simpler substances. This process, called decomposition, is vital for mineral cycling, as decomposers convert complex organic material into simpler forms, releasing minerals into the soil. 
• Bacteria and fungi, functioning as osmotrophs, absorb the decomposed organic matter, contributing to the renewal of soil resources. This efficient recycling system ensures that minerals are made available to producers for continued growth, highlighting the significance of decomposers in maintaining ecological balance.

4.0Trophic Levels

• In the ecosystem every organism is arranged in a series in which food energy is transferred through repeated eating and being eaten. It is called the food chain. In the food chain, energy flow is in the form of food.
• Flow of energy in a food chain, transfer is from one trophic level to the next trophic level.
• Four trophic levels are present in the ecosystem, because the level of energy decreases during the flow of energy from one trophic to the another trophic level.

First trophic level       [T1] =        Producers

Second trophic level  [T2] =        Primary consumers

Third trophic Level     [T3] =        Secondary consumers

Fourth trophic level    [T4] =        Top consumers

5.0Food Chains

In the ecosystem every organism depends on other organisms for food material and all organisms are (Plants, herbivores, carnivores) arranged in a series in which food energy is transferred through repeated eating and being eaten. It is called food chain. In the food chain, energy flow is in the form of food. In a food chain, food material or food energy transfer is from one trophic level to the next trophic level.

Types of Food Chains

Grazing Food Chain : This type involves the transfer of energy and nutrients from plants (producers) to herbivores (primary consumers), and then to carnivores (secondary and tertiary consumers).

Detritus Food Chain:  In this chain, the energy flow begins with dead organic matter (detritus) and is processed by decomposers (detritivores and decomposing bacteria and fungi) before reaching higher trophic levels.

For example: Dead organic matter → Decomposer bacteria and fungi 

Note :

• In detritus food chain energy flow is rather very slow yet magnitude of energy is great.
• In mangrove vegetation this food chain goes up to big organisms.
• Dead mangroves leaves → Bacteria & fungi → Aphids, molluscs, crabs, nematodes → Small fishes → Tiger.

Parasitic Food Chain : This food chain also starts from producers or by consumers but in successive order it goes from big organisms to the smaller organisms. For example: Tree  → Bird  → parasite. 

6.0Food Web

• In a big ecosystem many food chains are interlinked together on different trophic levels to form food web. In the food web transfer of food energy is unidirectional but from many different alternative pathways. In food web members of a particular trophic level obtain their food according to their choice and taste but that type of facility is not present in the food chain. It means they have more than one option or alternative for getting food.
• As much as the food web is complex that ecosystem is more permanent or stable, such type of ecosystem is not destroyed naturally and continues for long time. This ecosystem is not affected by loss of any organism of any particular trophic level. Those ecosystems which have simple food web are not very stable; it means that they can be finished at any time, if there is a change in any particular trophic level.

7.0Energy Flow Through Different Trophic Levels