Ecology can be studied at different levels, from a single living thing up to a whole habitat and the environment around it.
An organism is one individual living thing, such as a single fox. A population is all the organisms of one species living in an area at the same time, for example all the foxes in a wood. A community is all the populations of different species living together in the same area, such as the foxes, rabbits, grass and insects in the wood.
An ecosystem is the community together with the non-living, abiotic parts of the environment, such as the soil, water, light and temperature. So the levels go from organism, to population, to community, to ecosystem. Each level includes the one before it.
The ecosystem is the interaction between the living community and its non-living surroundings, which is why materials can cycle through it.
