Environments are always changing. Some changes occur naturally (examples include droughts, disease outbreaks, or forest fires sparked by lightning). Other changes are caused by human activity (examples include establishing conservation areas, passing laws to control pollution, clearing forests for agriculture or construction, applying chemicals to lawns and crops, burning fossil fuels, etc.).
All organisms depend on the living and nonliving features of the environment for survival.
When the environment changes, some organisms survive and reproduce, and others die or move to new locations.