Ecology is not limited only to the forces of nature because humans are an integral element of the web of physical and biological systems. The term ecology denotes the web of physical and biological systems and processes of which humans are one element.

Over time, ecology has been modified by human action. What appears to be a natural feature of the environment — such as aridity or flood-proneness — is often produced by human intervention. For instance, deforestation in the upper catchment of a river may make the river more flood-prone. Climate change brought about by global warming is another instance of the widespread impact of human activity on nature.

Over time, it is often difficult to separate and distinguish between the natural and human factors in ecological change. Just as nature shapes society, society shapes nature.