Ecology & Food Chains
Ecology and the Environment
The Vocabulary of Ecology
Ecology is the branch of biology that studies how organisms interact with each other and with their environment. The subject has its own set of precise terms, and many exam questions hinge on using them correctly.
Five terms you need to know
| Term | Meaning | Example |
|---|---|---|
| Population | A group of organisms of the same species living in the same area at the same time | All the grey squirrels in Hyde Park |
| Community | All the populations of different species living in the same area at the same time | All the squirrels, robins, oak trees, foxes, worms and mushrooms in Hyde Park |
| Habitat | The place where an organism lives | A woodland; a pond; a coral reef; a damp log |
| Ecosystem | A community of organisms plus the non-living factors of the area, all interacting together | A whole woodland (organisms + soil + climate + light + water) |
| Biosphere | All the ecosystems on Earth combined | The entire global ecosystem |
The progression goes from small to large:
single organism → population → community → ecosystem → biosphere
Ecosystems vary hugely in size. A small ecosystem might be a garden pond; a large one might be the whole of the Sahara Desert.
Common exam question
Defining population, community and ecosystem
Question: State what is meant by the term ecosystem, or pick the statement that describes a community, or the term for all the organisms together with their environment (1 mark).
Asked in 3 of the 23 papers, with the definition of biodiversity set in one more. An ecosystem is the community plus its environment: all the living organisms and the non-living conditions of an area together. A community is all the different species living in the area; add the environment and it becomes an ecosystem, keep only one species and it is a population. The wrong options in the multiple-choice versions are exactly these neighbours: an option listing every biotic and abiotic factor of an area describes an ecosystem, not a community, and a habitat is the place without its organisms. Biodiversity is the variation shown by the organisms in an ecosystem: the number of different species and the abundance of each.