How we change Mexico´s ecosystem

In Mexico, old civilizations such as olmecas, mayas, aztecas, etc were based on the modification of natural ecosystems introducing the agriculture. This is one out of two main activities, they did to change natural ecosystems. These civilizations that lived in our country gived the world more than 80 species of cultivated plants, such as corn, beans, chilli, tomato, vanilla, tabaco, etc. The second main activity old civilizations did, was to transformed a natural ecosystem into a place to live, to plant vegetables and to raise animals. In our days we have communities known as rural and urban communities.
A rural community is a small gruop of people, its more important activity is agriculture, and it has less than 2,500 residents. An urban community is bigger than a rural it has more than 2,500 residents and they use commerce and industry as a main activity. As the grow they expand and they change natural ecosystems by building houses, buildings, industries, pipes for w0ater, lines of communication, energy plants, etc. When an urban community reaches 50,000 residents or more it´s called a city.
Urban communities have more and a better quality of services, such as schools, medical center, transportation, access to clean water, electricity and more options to work as a profesional, than a rural community.in some cases this causes more traffic and pollutions wichs affects the residents.