An ecosystem is a community of living organisms and non-living components that work together. An ecosystem can be something as large as a desert or something as small as a log in which organisms live. The living parts of an ecosystem such as plants, animals, microorganisms or insects are called biotic factors. The non-living parts of an ecosystem such as water, air, sediment or rocks are called abiotic factors. Ecosystems are made up of both biotic and abiotic factors. The community of living and non-living parts of an ecosystem will vary from ecosystem to ecosystem. The biotic and abiotic factors in a desert, for example, will likely be different than the biotic and abiotic factors in a tropical rainforest.