A community is a group of different species living in the same area ^{3 1 2 4 5}. An ecosystem is all of the organisms in an area plus the nonliving parts of their environment ^{1 2 5}. Organisms interact with both living and nonliving parts of their ecosystem ¹. Organisms depend on these interactions in order to survive and have offspring ¹.

Community ecology examines how coexisting organisms interact and compete in a particular niche or geographical location ⁴. Community ecologists focus on interactions between populations and how these interactions shape the community ⁵.

Ecosystem ecology often focuses on flow of energy and recycling of nutrients ⁵.