Ecology is the study of organisms interacting with their environment.
Principle 1: Energy Flows through Trophic Levels
Ecology can be thought of as the flow of energy and nutrients among different organisms in an environment. Here’s a good video that explains it:
Principle 2: Individual —> Population —> Community —> Ecosystem
Principle 1 only talked about communities. On a broader level, you have other levels of the environment.