Communities
These are important key terms:
- An ecosystemThe living organisms in a particular area, together with the non-living components of the environment. is the interaction between a communityAll the organisms that live in a habitat (plants and animals). of living organisms and their environment.
- A community is two or more populationAll of the members of a single species that live within a geographical area. of organisms.
- An ecosystem is two or more populations of organisms (usually many more) in their environment.
- A population is all the organisms of the same or closely related speciesA type of organism that is the basic unit of classification. Individuals of different species are not able to interbreed successfully. in an area.
Levels of organisation within an ecosystem
Individual organism
鈻
Population of individuals
鈻
Community of populations
鈻
Ecosystem describing communities in their environment
Organisms within an ecosystem are organised into trophic levels.
| Producer | Plants and algae, which photosynthesise. |
| Primary consumer | Herbivores, which eat producers. |
| Secondary consumer | Carnivores, which eat primary consumers. |
| Tertiary consumer | Carnivores that eat secondary consumers. |
| Producer |
|---|
| Plants and algae, which photosynthesise. |
| Primary consumer |
|---|
| Herbivores, which eat producers. |
| Secondary consumer |
|---|
| Carnivores, which eat primary consumers. |
| Tertiary consumer |
|---|
| Carnivores that eat secondary consumers. |
Interdependence
All organisms in an ecosystem depend upon each other. If the population of one organism rises or falls, then this can affect the rest of the ecosystem.
A simple food chain is:
grass 鈫 rabbit 鈫 fox
If the foxes in the food chainA sequence (usually shown as a diagram) of feeding relationships between organisms, showing which organisms eat what and the movement of energy through trophic levels. above were killed, the population of rabbits would increase because they are no longer prey to the foxes. As a result, the amount of grass would decrease because the increased population of rabbits would be eating it.
Often very small changes to ecosystems have large consequences, which can be difficult to predict. This means that all the organisms in an ecosystem are dependent upon each other. We call this interdependenceRefers to the fact that all organisms that live in an ecosystem depend upon each other, for food, protection, shelter, etc, in order to survive..
Competition
All photosynthesisA chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. plants and algae in an ecosystem compete for light, space, water and minerals from the soil. Animals in an ecosystem compete for food, mates and their territory. Organisms which have more of these resources tend to grow more healthily and are more likely to have offspring.
Competition can be interspecific or intraspecific depending on whether organisms from different species or the same species are competing for resources. Competition helps regulate the size of populations.
Stable communities
A stable community is one in which the size of the populations of all species remain relatively constant over time. In the example above the amount of grass, and the numbers of rabbits and foxes all remain relatively constant. The different populations are living in a healthy balance with their environment.
More guides on this topic
- What happens during photosynthesis? - OCR 21st Century
- How do producers get the substances they need? - OCR 21st Century
- How do producers transport substances they need? - OCR 21st Century
- How are levels maintained within an ecosystem? - OCR 21st Century
- How are populations affected by conditions in an ecosystem?
- Sample exam questions - living together - OCR 21st Century