The interaction or relationship between living and non-livings beings in a natural environment forms an ecosystem. 

All the organisms in an ecosystem are dependent on each other some way or the other and linked together by transfer of energy and material.

Human environment is hence the interaction between human beings and the environment. The difference between human-made and human environment is that the former comprises non-living things, a result of human activities while the latter is the interaction between human and the environment.

Human beings usually modify the natural environment as per their needs. Once the human settlements started, humans began the trading of articles amongst themselves. This was called as the barter trade.