An ecological community describes the interactions of two or more species which are occupying the same geographic area and are intereacting in that area. For instance, a community in a single meadow might include the grasses and plants that grow there, the insects and mice that feed on the plants, the small birds that feed on the insects, and the foxes and birds of prey that feed on the mice and the smaller birds.
The concept of an ecosystem encompasses a number of communities and the abiotic resources that they depend on. The exact boundaries of an ecosystem can be defined in many ways. Our meadow from the example above might be part of a watershed that also includes forests, mountains, lakes, and streams. The watershed could then be studies as an ecosystem.