For instance, if we intend to kill any kinds of pests or bugs by using pesticides, such as DDT, the toxic residues of this chemical will fall to the ground and is dissolved into the river, and then the plankton collects this DDT, which will then be eaten by the fish. Afterwards, the birds will be exposed to this toxin by eating fish in turn. Finally, the ecosystem will be detrimental to all kinds of creatures on earth. Another example related to this cause is hunting animals for their skins or furs, which is usually illegal. Killing these rare animals means destroying the food chains as well. When some types of animals such as bears or tigers are hunted in a vast number, other types of creatures would be increasing at an imbalanced rate.