Energy flow is the flow of energy through living things within an ecosystem. The source of all energy exist in earth is the sun. The flow of energy in the ecosystem is always unidirectional (linear). The energy flow obeys the first and second law of thermodynamics. The 1st Law of thermodynamics state that Energy cannot be created or destroyed but can be transformed from one form to another. The 2nd Law thermodynamics state that When energy is converted into different forms, its capacity to perform useful work diminishes.
The living plants capture the sun energy and transferred them through food chain and food web. But what are food chain and food web we often see?
A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another. The levels in the food chain are producers, primary consumers, higher-level consumers, and finally decomposers. Food Chains are generally classified into two: A grazing food chain and detritus food chain-
(a) Grazing food chain: It includes eating of a plant by an animal and eating of an animal by another. The food chain always starts with the green plants.
(b) Detritus Food Chain: It starts from dead organic matter (detritus) and goes through decomposers (bacteria, fungi) to the detritus feeders (earthworms) and then to carnivores feeding on them.
A food web is a concept that accounts for the multiple trophic (feeding) interactions between each species. Two general types of food webs are often shown interacting within a single ecosystem. A grazing food web has plants or other photosynthetic organisms at its base, followed by herbivores and various carnivores. A detrital food web consists of a base of organisms that feed on decaying organic matter (dead organisms), including decomposers (which break down dead and decaying organisms) and detritivores (which consume organic detritus).
A trophic level is the group of organisms within an ecosystem which occupy the same level in a food chain. There are five main trophic levels within a food chain, each of which differs in its nutritional relationship with the primary energy source. The primary energy source in any ecosystem is the Sun. When an organism dies it is converted to detritus. It then serves as an energy source for decomposers.
The term ecosystem productivity is referred to as the amount of organic matter accumulated in any unit time. It is of two types: Primary Productivity and Secondary Productivity.
Primary productivity: It is the rate at which biomass or organic matter is produced per unit area over a time period by plants during photosynthesis. It can be divided into gross primary productivity (GPP) and net primary productivity (NPP).
Secondary Productivity: Secondary productivity is defined as the rate of formation of new organic matter by consumers. Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers).
Ecological pyramids are the graphical representation of the relationship between the different living organisms at different trophic levels. It was given by G.Evylen Hutchinson and Raymond Lindeman. Ther are three Ecological pyramids which are-
(i) Pyramid of Numbers: It represents the relationship between number of individuals of primary producers and consumers at different trophic levels. It can be upright or inverted. In an upright pyramid of numbers, the number of individuals decrease from lower to higher trophic level. Example: In a grassland ecosystem. In an inverted pyramid of number, the number of individuals increase from lower to higher trophic levels. Example: A large number of birds feeding on a single tree.
(ii) Pyramid of Biomass: Biomass id the total mass (in g. dry weight) of living organisms in an area at a particular point of time. A pyramid of biomass is obtained when the rectangles used to construct the pyramid represent the masses of organisms at each trophic level. Pyramid of biomass can be upright (e.g. in grassland ecosystem) or inverted. Inverted pyramids can occur in aquatic ecosystems. This happens because in aquatic ecosystems producers are tiny phytoplankton. Thus, consumer biomass exceeds producer biomass.
(iii) Pyramid of Energy: It represents the total amount of energy used at each trophic level per unit of area per unit of time. It thus shows how energy flows from one trophic level to another in an ecosystem. A pyramid of energy is always upright
