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close this bookBasic Concepts in Environment, Agriculture and Natural Resources Management: An Information Kit (IIRR, 1993, 151 p.)
close this folderEcological basics
View the documentEcosystem degradation
View the documentHabitat and niche
View the documentThe food chain
View the documentBiological magnification
View the documentNitrogen cycle
View the documentSociety and the carbon-oxygen cycle
View the documentHealth consequences of environmental degradation
View the documentPopulation and the environment

The food chain

The food chain


· All lives exist in an ecological system. Organisms are interrelated by many things. One important relationship among plants and animals is the concept of food chain. Transfer of food energy in which one type of organism consumes another is referred to as the food chain.

· Plants receive energy from the sun and convert it into chemical energy through the process of photosynthesis. Similarly, plants get food from the soil. In both cases of energy transfer from the surf end the soil to the plans, some energy is lost as heat and cannot be used to make the living matter of the plant. Similarly, when plants are eaten by animals, some energy is lost in the transfer of energy from the plants to the animals. Typically, only about 10 percent of the energy is effectively transferred at each link of the food chain. This process can be represented by what is known as the food pyramid.

· All organisms that share the same general types of food in a chain are said to be at the same trophic level. Thus, green plants (producers) occupy the first trophic level, herbivores (primary consumers) occupy the second trophic level, carnivores (secondary consumers) which eat the herbivores occupy the third trophic level and top or secondary carnivores (tertiary consumers)—those that eat other carnivores - occupy the fourth trophic level. The classification of species into trophic levels is based on the function, rather than the species itself. Humans are considered to be omnivores, eating plants, therefore, functioning as a herbivore; and, eating animals, therefore, functioning as a carnivore.

· Food chains are not isolated sequences but are interconnected with one another. The complex series or network of many interconnected food chains is called a food web. Food webs are an important factor for understanding/he importance of maintaining plant and animal diversity in order to protect the interlocking nature of food chains and food webs. As plant and animal species are lost, breaks can occur in the food chain and food web.

· The most obvious form of species interaction in food chains and webs is predation. An individual organism of one species, known as the predator, captures and feeds on parts or all of an organism of another species, the prey. Humans act as predators whenever we eat any plant or animal food.

· An important principle affecting the ultimate population size of an omnivorous species, such as humans, emerges from a consideration of the loss of available energy at successively higher trophic levels in food chains and webs: The shorter the food chain, the less the loss of usable energy. This means that a larger population of humans can be supported if people shorten the food chain by eating grains directly (for example, 1 ha rice = 10 people) rather than eating animals that feed on the grains (grain - cattle - human).