What Are the Levels of Organisation in an Ecosystem?

The levels of organisation in an ecosystem are organism, population, community and ecosystem, from smallest to largest. An organism is one living thing. Each level groups together more living things, until the ecosystem also includes their non-living environment and the interactions within it.

What does each level mean?

• Organism: one individual living thing, such as a single oak tree.
• Population: all the organisms of one species living in an area, such as the oak trees in a woodland. A species is a group of similar organisms.
• Community: the populations of different species living together in an area. A woodland community includes trees, insects, birds and microorganisms.
• Ecosystem: a community interacting with the non-living parts of its environment. In a woodland, these include light, temperature, water and soil.

A habitat is the place where an organism lives. Organisms in the same habitat can depend on one another: birds may eat insects, for example, while plants may depend on insects for pollination. They can also compete for resources. Plants often compete for light, water and space; animals may compete for food or mates. These relationships help explain why a change to one part of a community can affect other organisms.

Pond example

Picture one frog in a pond: that is an organism. All the frogs living in the pond form a population. The frogs, pond plants and other living things together form a community. When you include how those living things interact with pond water, light and temperature, you are describing the ecosystem. The living parts are called biotic; the non-living parts are abiotic.

Common exam mistake: a community includes living populations, but it does not include the non-living environment. Include both when describing an ecosystem. Also, do not call every living thing in a pond one population: a population contains organisms of one species.