Throughout time, humans have learned to exist in many locations on the earth. The interaction of humans with the environment in these locations has often brought major changes in that environment. Some changes were good, some were bad. Many times the bad changes were caused by humans making too much of a change in the environment, by using or abusing the natural resources (anything found in nature) present.
Every location where the human race has lived contained a community of plants, animals, insects, and other natural resources. A community of organisms, other natural resources, and their influence on each other is called an ecosystem. The plants and animals existing in an ecosystem are those most adapted to that particular environment.
Changing or using natural resources will affect the entire ecosystem, since an imbalance in the system is created. Ecosystems naturally change with time. In most cases, the change does not completely destroy the ecosystem, because a new, slightly different ecosystem can be created with the natural resources that are currently in place. Ecosystems can be destroyed, however, if the change is made too quickly.
Ecosystems can be large or small. An example of a small ecosystem is a pond. A large ecosystem could be a tropical rainforest. There are usually no boundaries between ecosystems - changes can only be seen over a long distance.