What affect might the elimination of any organisms have on an ecosystem?

The elimination of an organism in an ecosystem takes out all balance. There may be an overpopulation of some organisms, and an underpopulation of others. For an example, if rabbits were taken out of the food chain, there would be an overpopulation of grass, and underpopulation of what eats rabbits.

Humans have survived and thrived in mexico city by using technology to create greater access to land. when the spanish conquered the aztec capital, tenochtitlan, in the 16th century, they built mexico city by draining the lakes and filling in the lake water to create more arable land for agriculture. this technique of land reclamation has continued to be fundamental to human civilization in mexico city. 

Ineed you to put up a picture of the map so i can you as much as possible.