Ecosystems differ in composition and extent. They can be defined as ranging from the communities and interactions of organisms in your mouth or ① those in the canopy of a rain forest to all those in Earth’s oceans. The processes ② governing them differ in complexity and speed. There are systems that turn over in minutes, and there are others ③ which rhythmic time extends to hundreds of years. Some ecosystems are extensive (‘biomes’, such as the African savanna); some cover regions (river basins); many involve clusters of villages (micro-watersheds); others are confined to the level of a single village (the village pond). In each example there is an element of indivisibility. Divide an ecosystem into parts by creating barriers, and the sum of the productivity of the parts will typically be found to be lower than the productivity of the whole, other things ④ being equal. The mobility of biological populations is a reason. Safe passages, for example, enable migratory species ⑤ to survive
* canopy: 덮개 ** basin: 유역