The sun is the ultimate source of energy for all living organisms. Autotrophs capture solar energy and convert it to chemical energy. Then the autotrophs and the heterotrophs utilize the autotrophs' chemical energy. Now it is time to look at the bigger picture-how living organisms interact with each other and their surrounding environment while cycling chemicals and transferring energy. This is what ecosystems are all about, and it is not a static proposition.
Ecosystems are dynamic and constantly changing, just as populations and communities are.
Many of the changes occurring now, unfortunately, are harmful ones brought about by human interference and pollution.