The main source of energy in almost all natural ecosystems is radiant energy from the sun.
Studies suggest that ecosystems generally fix 3 percent or less of sunlight, and that for most ecosystems this figure is probably less than 1 percent.
Humans are part of the environment and thus impact, and are impacted by, ecosystems.
A river, a swamp, a meadow, and a cave are all examples of ecosystems.
Different ecosystems are often separated by geographical barriers, like deserts, mountains, or oceans, or are isolated otherwise, like lakes or rivers.
Clearly, the study of ecosystems and human impacts is important for creating a sustainable environment for future generations.
All large rivers in the temperate zone have been altered for human use, as have most of the world's large river floodplain ecosystems.
Tansley expanded on the term in his later work, adding the ecotope concept to define the spatial context of ecosystems (Tansley 1939).