Food Chains and Food Webs

Food Chain:

• Ecosystems have an hierarchy of feeding relationships (trophic levels) that determine the pathway of energy flow in the ecosystem. The energy flow in the ecosystem can be illustrated as a Food chain.

• Sun is the ultimate source of energy in ecosystems. Producers or autotrophic organisms convert the solar energy into chemical or organic energy during photosynthesis. 

• This is the source of food for heterotrophic organisms and these animals may in turn be eaten by other animals. In this way energy is transferred through series of organisms. Such a sequence is called food chain or grazing link in the ecosystem. 

• Each stage of the food chain is known as a trophic level. Producers occupy the first trophic level. The second trophic level is occupied by the primary consumers and third is occupied by secondary consumers and so on.

• In some ecosystems, as much as 80% of primary production is not eaten by primary consumers. Instead, decomposer organisms consume plant materials. This type of food chain is konwn as detrital food chains, (eg. Tropical forest ecosystems).

Producers, Consumers and Decomposers

The biotic community of any ecosystem can be divided simply into producers, consumers and decomposers.

Producers:

Producers or autotrophs are organisms that make their own organic material from simple inorganic substances. For most of the biosphere the main producers are photosynthetic plants and algae that synthesis glucose from carbon dioxide and water. The microscopic algae and blue-green bacteria are the main producers in an aquatic ecosystem and are known as phytoplankton. 

The glucose produced is used both as an energy source and combines with other molecules from the soil to build biomass. It is this biomass that provides the total theoretical energy available to all non photosynthesising organisms in the ecosystem.

Energy flow in the Ecosystem

The study of energy flow through the ecosystem is called energitics. It includes energy transformation which occurs in the ecosystem. It involves;

1. Quantity of energy reaching to the ecosystem.
2. Quantity of energy trapped by green plants and its conversion of chemical energy.
3. Quantity and path of energy flow from the green plants to organisms of different trophic level.

From sun's, energy which reach to the earth, 40% is reflected immediately from the clouds or dusk etc. 15% is absorbed and converted into heat energy. 45% penetrates to the earth's surface. Out of it 5% is converted into chemical energy by photosynthesis. 

Autotrophs capture the solar energy and provides to the other organisms in the ecosystem. The chemicals found in living organisms are derived from abiotic components (air, water, soil) and they return back by decomposition. Bacteria and fungi bring about decomposition, obtaining energy from waste products and dead organisms in the process.

The Transformation of Energy

The transformations of energy in an ecosystem begin first with the input of energy from the sun. Energy from the sun is captured by the process of photosynthesis. Carbon dioxide is combined with hydrogen (derived from the splitting of water molecules) to produce carbohydrates (CHO). Energy is stored in the high energy bonds of adenosine triphosphate.

The prophet Isaah said "all flesh is grass", earning him the title of first ecologist, because virtually all energy available to organisms originates in plants. Because it is the first step in the production of energy for living things, it is called primary production. Herbivores obtain their energy by consuming plants or plant products,carnivores eat herbivores, and detritivores consume the droppings and carcasses of us all. 

Concept of an Ecosystem

The term ecosystem genaerally refers to all biotic and abiotic components and their interarction with each other, in some defined area. The ecosystem was proposed by A. G. Tansley in 1935. An ecosystem consists of the biological community that occurs in some locale, and the physical and chemical factors that make up its non-living or abiotic environment. There are many examples of ecosystems; a pond, a forest, an estuary, a grassland. The boundaries are not fixed in any objective way, although sometimes they seem obvious, as with the shoreline of a small pond. Usually the boundaries of an ecosystem are chosen for practical reasons having to do with the goals of the particular study.