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In nature, some beings may play various roles in different food chains. When we eat an apple, for example, we play the role of primary consumers. Already eating a steak, we are secondary consumers, because the ox, which eats the grass, is primary consumer.
Many other animals also have varied diets. An organism can feed on different living things and can serve as food for several others. The result is that food chains intersect in nature, forming what we call food web.
In food webs, the same animal may play different roles depending on the chain involved. In the web shown in the diagram below (follow the arrows) the hawk occupies both the secondary and tertiary consumer roles.
|Producers||Primary consumer||Secondary Consumers|
Plants, Fruits and Seeds
|Producers|| Consumer |
|Plants, Fruits and Seeds||Woodpecker||Sucuri||Hawk|
Plants never change their role: they are always producers. And all producers and consumers, are linked to decomposers, which allow the recycling of organic matter in the environment.
Substance accumulation in the food chain
In the early 1950's, on a lake in the United States, a insecticide, a chemical that destroys mosquitoes. The amount applied was minimal.
Five years later, however, dead loons began to appear on the lake. Research has shown that these birds died intoxicated by the insecticide. The researchers found that the insecticide had entered the food chain. First, the microscopic algae in the lake absorbed the insecticide; later the small fish fed on these algae; the bigger fish ate the smaller ones; and finally the loons ate the bigger fish.
The insecticide used in the lake belonged to a group of substances that remained in the environment for hundreds of years without decomposing, or decomposing very slowly. Likewise, when ingested, these substances usually take a long time to be eliminated by the body.
Other examples of elements that the organism of living beings has difficulty decomposing and eliminating are the lead it's the Mercury. If ingested frequently, these substances accumulate in the body and cause disease.
In certain regions of Brazil, prospectors use mercury to separate gold from sand. Some of the mercury spreads in water and gets lost. As a result, the prospectors themselves risk direct contamination and, furthermore, river waters become dangerous with a high mercury rate. This mercury may over time deposit in the body of fish-eating people.