A food chain represents the direction of flow of matter and energy in a part of the ecosystem. An ecosystem has a number of food chains. Each food chain consists of producers and consumers of food and is very simplified. In a food chain, each consumer is related to only one producer and hence is very restricted in nature. Given this restrictive nature of food chain, removal of any level or animal will disrupt the entire food chain. For example, in grasslands deer eats grass and tiger eats deer. If we kill all the deer by hunting, there would be no consumer of the grass and it would grow unrestrained (limited only by environmental factors such as weather, nutrition, etc.). On the other hand, the tiger will have no food to eat and hence will die out. Hence, removal or change of any element in the food chain will disrupt it (or disturb it to large extent).
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