There is this really great book called EXTINCTION by the Ehrlichs(?)...which starts out with a beautiful analogy about the environment. It starts off with this guy who removes rivets (screws) from an airplane wing so that he could sell them for profit. Each rivet/screw represents a unique species that plays an important role in our ecosystem. The loss of each one has an adverse effect on the whole structure. It is true that such effects may or may not have an immediate recognizable effect on us but that does not mean that it is not happening. Also, we humans, have proven that we are really self centered that we do not recognize the damage that we are doing unless it hits us in the face. There are countless examples of chain reactions in the ecosystem due to a loss of an integral species. For example, (although I am no longer certain about the details) due to the misuse of a pesticide by farmers in rural Peru, an outbreak of more resistant  pests evolved. The farmers in reaction started to use more pesticides which affected the other species that naturally feed on and control these pests. The situation got so bad that it escalated to such an extent that cats which controlled the rat population died out because they got the higher dose of the poisonous pesticide in their system. Finally, (believe it or not) they had to fly cats to the area and dropped them from helicopters...thus it did rain cats that day in Peru.
In what ways does wildlife extinction impacts our world.?