Ecosystem part-3,#food chain & food web In#Kannada and English#NEET Biology by#BG Basavana Gowda T S

FOOD CHAIN In ecosystem, every organism depends on other organisms for food material and all organisms are (herbivores to carnivores) arranged in a series in which food energy is transferred through a repeated series of 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 from one trophic level to the next trophic level. Four trophic levels are present in the ecosystem because level of energy decreases during the flow of energy from one trophic to 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 In nature, three types of food chains are present : Grazing food chain, parasitic food chain and detritus food chain. NOTES There are five trophic levels found in highly complex ecosystem in which tertiary consumer is present in between the secondary consumers and top consumers. Then the fifth trophic level (T5) is formed by the top consumer. Shorter food chains will provide greater energy. Generally the decomposers (bacteria and fungi) are not included in the food chain but when included then there are included as the last tropic level. GRAZING FOODS CHAINS OR PREDATORY FOOD CHAIN Most of the food chain in nature are of this type. This food chain begins with producers (plants) and in successive order it goes from small organism to large organism. Aquatic ecosystem Grasslamd ecosystem PARASITIC FOOD CHAIN This food chain also starts from producers but in successive order it goes from big organism to the smaller organism. Tree ecosystem NOTES Both grazing and parasitic food chains are directly dependent on solar radiation (as a primary source of energy) and have rapid energy flow. DETRITUS FOOD CHAIN OR SAPROPHYTIC FOOD CHAIN This food chain begins with decomposition of dead organic matter by decomposers so it is also known as saprophytic food chain. In this food chain, primary consumers are bacteria and fungi. In mangrove vegetation, this food chain goes up to big organism. Dead mangroves leaves → Bacteria & fungi → Amphipods, molluscs, crabs, nematodes → Small fishes → Fish eating birds. In detritus food chain, energy flow is rather very slow yet magnitude of energy is great because vast number of decomposers are involved. Detritus food chain does not depend on light. FOOD WEB Food web, refers to the group of interconnecting food chains in a particular community. In a food web, transfer of food energy is unidirectional but from many different alternative pathways. In a food web, members of a particular trophic level obtain their food according to their choice and taste. It means they have more than one option or alternative for getting food. As much as food web in complex ecosystem is more permanent or stable, such type of ecosystem is not destroyed naturally and continues for a 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. HOMOEOSTASIS Ecosystem is a dynamic system because continuous interaction is going on in between abiotic or biotic components, so ecosystem is present in an equilibrium position. Ecosystem is also self maintainable and self regulatory system. It means an ecosystem maintains a balance in between different trophic levels. Each trophic level controls the other trophic level and if any change takes place in any trophic level of ecosystem, the other trophic levels of this ecosystem may react according to it. So, ecosystem always remain in equilibrium. This feature of the system is known as homeostasis.