Ecosystem, it's structure and functions

<!> The notion of an ecosystem is theoretical : it is multiscale, meaning that it can be applied to varying-sized portions of the biosphere, such as a pond, a meadow, or a dead tree. A smaller unit is called a microecosystem. An example of a microecosystem would be the species that have colonized a submerged rock. A mesoecosystem might be a forest, and a macroecosystem might be a region and its watershed.