Ecologists describe living things at different levels of organisation, from a single organism up to a whole ecosystem. The smallest level is the individual organism, which is one living thing, such as one frog.
All the individuals of one species living in the same area at the same time form a population. All the frogs in a pond are a population. A population contains only one species and is made up of individual organisms.
All the populations of different species living in the same area form a community. The frogs, fish, insects and water plants in the pond make up the pond community. A community contains many species that live together and affect each other.
An ecosystem is a community together with the abiotic factors of its surroundings, such as water, light, temperature and soil, and the way they interact. The whole pond, with its community and its abiotic conditions, is an ecosystem. In order from smallest to largest the levels are: individual organism, population, community, ecosystem.
