What is an ecosystem?
An ecosystem is a community of living things, such as plants, animals and microbes, interacting with each other and with their physical environment, like water, soil and climate.
Ecosystems can be as large as a rainforest or an ocean, or as small as a pond or a rotting log. In every ecosystem, energy flows from the Sun to plants, which make food through photosynthesis. Plant-eating animals eat the plants, predators eat the plant-eaters and decomposers break down dead material, returning nutrients to the soil.
The living parts of an ecosystem are called biotic factors, and the nonliving parts, such as sunlight, temperature, rocks and water, are called abiotic factors. A change in one part, like a drought or the loss of a species, can affect many others.
Keystone species
Some species have an especially large effect on their ecosystem. When gray wolves were brought back to Yellowstone National Park in 1995, they reduced the number of elk. This allowed trees along rivers to recover, which helped beavers, birds and fish. Such species are called keystone species.
Did You Know?
The term ecosystem was first used by British ecologist Arthur Tansley in 1935.