Ecosystems are defined as a unique grouping of the living environment and with the non-living environment, where the living environment interacts with each other and with the non-living environment. An ecosystem must occupy a specific unit of space, or a defined area of Earth's surface.
I will begin by picking apart this definition and describing it in more detail.
Unique. The combination of living and non-living environments must be unique. What does this mean? It means every ecosystem must have a unique combination of non-living materials and living materials. If either changes significantly, it becomes a separate ecosystem.
Living Environment. The living environment consists of plants, animals, microbes, fungus--anything that is defined as life by biologists. Collectively, all the species on Earth, along with all their environments, make up one vast ecosystem known as the biosphere. The biosphere is then broken down into biomes or landscapes , which are a group of ecosystems that share similar climatic conditions. Examples include deserts, arctic tundra, tropical rain forests, and praries.
Non-living Environment. The non-living environment consists of rocks, soils, sediment, water, and gasses. Collectively, these are known as the hydrosphere (ice and water), lithosphere (rock, soil, sediment), and the atmosphere (air and gasses).
Ecosystems represent the product of the interaction between Earth's major systems (or spheres). Changes in one system affect other systems. Energy from the sun drives these systems and provides energy for systems to interact. (Wright; Pearson/Prentice Hall).
Interaction. The living and non-living environment does not act independently. Each is interdependent on the other. Changes in the non-living environment affect the living environment and visa versa. On the local level, changes in one ecosystem affect nearby ecosystems. Cutting down an acre of forested land impacts the adjacent ecosystems.
Occupy a Specific Place. Ecosystems have to occupy a defined geographic area. The boundary between different ecosystems should be mappable. Regardless of how humans define boundaries between ecosystems, they all remain interconnected and interdependent. There are seldom sharp boundaries between ecosystems, one ecosystem usually gradually transitions to the next ecosystem.