By the end of this lesson
- Define population, community, habitat and ecosystem.
- Classify an ecological description at the correct level.
- Explain why ecosystems include abiotic as well as biotic components.
BIG QUESTION
Is a pond one population, one community or one ecosystem?
The same pond can be described at each level; the correct term depends on whether the physical environment and other species are included.
Populations and communities are about organisms
A populationAll the organisms of one species living in the same habitat at the same time. is all the organisms of one species living in the same area at the same time. The frogs of one species in a pond form one population.
A communityAll the populations of different species living in the same habitat at the same time. is all the populations of different species living and interacting in the same area. The frogs, pondweed, water fleas, algae and bacteria in the pond together form the community.
A habitat is where an organism lives
A habitatThe place where an organism lives, providing the conditions and resources it needs. is the place where an organism lives, providing the conditions and resources it needs. A habitat can be large, such as a woodland, or small, such as the underside of a log.
Different species in one ecosystem may occupy different habitats within it, for example the mud at the bottom of a pond and the surface film.
An ecosystem adds the non-living environment
An ecosystemA community of organisms together with the non-living (abiotic) parts of their environment. is a community of organisms interacting with each other and with their non-living (abiotic factorA non-living factor in an ecosystem, such as temperature, light intensity, water or soil pH, that affects the organisms living there.) environment, such as water, light, temperature and minerals.
Energy flows through an ecosystem and nutrients cycle within it, so an ecosystem is defined by interactions rather than by a fixed boundary. Its edge is usually chosen by the investigator for a stated purpose.
Levels of ecological organisation
Each term adds something to the one before it.
| Term | What it includes | Pond example |
|---|---|---|
| Population | One species in one area at one time. | All the common frogs in the pond. |
| Community | All populations of all species in the area. | Frogs, pondweed, water fleas, algae and bacteria. |
| Habitat | The place where an organism lives. | Shallow, weedy margins used by frog tadpoles. |
| Ecosystem | Community plus abiotic environment, and their interactions. | The pond organisms with its water, mud, light and temperature. |
Language that earns precision
- population
- All the organisms of one species living in the same area at the same time.
- community
- All the populations of different species living and interacting in the same area.
- habitat
- The place where an organism lives.
- ecosystem
- A community and its abiotic environment, interacting together.
- abiotic
- Non-living, such as temperature, light or pH.
- biotic
- Living, or caused by living organisms.
Common misconceptions
Claim: A population contains all the animals in an area.
Correction: A population is one species only. All species together form the community.
Claim: Habitat and ecosystem mean the same thing.
Correction: A habitat is where an organism lives; an ecosystem is the whole interacting system of organisms and abiotic factors.
Claim: A community includes the soil and water.
Correction: A community contains only living organisms. Adding the abiotic environment makes an ecosystem.
Match the answer to the command word
For population, always include “one species”, “same area” and “same time”.
Ask: one species or many? Living only, or living plus non-living?
Recall, apply, then justify
Define the term ecosystem.
Hint
Two parts: the living component and what it interacts with.
Suggested marking points
- A community of (different populations of) organisms.
- Interacting with (each other and) the abiotic/non-living environment.
A student counted all the dandelions on a school field. Explain whether this is a population or a community.
Hint
How many species were counted?
Suggested marking points
- It is a population.
- Because only one species was counted in one area (at one time).
Explain why an ecologist studying a rock pool must state the boundary of the ecosystem being studied.
Planning hint
Think about tides, mobile organisms and the flow of energy and nutrients.
What a strong design includes
- Ecosystems do not have fixed natural edges.
- The tide links the rock pool to the wider shore and sea.
- Mobile organisms such as birds or fish move in and out.
- Energy and nutrients enter and leave across the boundary.
- Population counts depend on which area is included.
- A stated boundary lets results be compared and repeated.