AQA A Level Biology

Revision Notes

7.4.1 Communities

The Definition of a Community

  • Species do not exist by themselves in their own isolated environment, they interact with other species forming communities
  • A community can be defined as:

Multiple populations (of different species) living and interacting in the same area

  • For example, a garden pond community is made up of populations of frogs, newts, pond snails, damselflies and dragonflies and their larvea, water beetles, water boatmen, pond skaters and many other species all living and interacting within the pond habitat


  • Communities interact with the non-living components of the environment they live in, forming ecosystems
  • An ecosystem can be defined as:

The interaction between a community (the living, biotic part) and the non-living (abiotic) parts of the environment

  • An ecosystem is a relatively self-contained community of interacting organisms and the environment they live in, and interact with
  • There is a flow of energy within an ecosystem and the nutrients within it are recycled (e.g. the carbon, nitrogen and phosphorus cycles)
  • There are both living (biotic) components and non-living (abiotic) components within an ecosystem
  • Ecosystems vary greatly in size and scale
    • Both a small pond in a back garden and the open ocean could be described as ecosystems
    • A human being could also be described as an ecosystem (there are thousands of species of bacteria living on and in every person)
  • Ecosystems vary in complexity:
    • A desert is a relatively simple ecosystem
    • A tropical rainforest is a very complex ecosystem
  • No ecosystem is completely self-contained as organisms from one ecosystem are often linked to organisms from another
    • For example, many birds species are able to migrate long distances to find food sources or breeding locations from various ecosystems

Example of an ecosystem

  • A forest is a perfect example of a complex ecosystem
  • There is a large community of organisms including trees, birds, small and large mammals, insects and fungi
  • The non-living components of the ecosystem include the soil, dead leaves, water from the rain and streams, the rocks and any other physical or chemical factors
  • The non-living components of the ecosystem influence the community of organisms

Levels of Organisation in an Ecosystem, downloadable IGCSE & GCSE Biology revision notes

Levels of organisation in an ecosystem


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top