Walk into any woodland, and you might notice a single red squirrel darting up an oak tree. However, that squirrel is just one small part of a much larger, interconnected biological system. Ecologists organise these living systems into a step-by-step hierarchy of increasing complexity.
At the base of the hierarchy is the , which is a single living organism belonging to a specific . A is defined as a group of similar organisms that can interbreed to produce fertile offspring.
When you group together all the of the same living in the same area (their ) at the same time, this forms a .
In reality, do not live in isolation. A is formed when all the of different live and interact together in the same area at the same time.
Finally, to step up to an , we must look beyond just the living organisms. An is formed by the interaction between the entire and its non-living physical environment.
To understand how these levels build upon one another, we can trace the hierarchy through two different environments:
| Level | Description | Woodland Example | Pond Example |
|---|---|---|---|
| A single living entity. | One red squirrel | One Great Crested Newt | |
| All members of one in an area. | All red squirrels in the woodland | All newts in the pond | |
| All different interacting in the area. | Red squirrels, oak trees, foxes, birds, and fungi | Newts, algae, fish, and pond snails | |
| interacting with the physical environment. | The forest ( + soil nutrients, rainfall, light) | The pond (organisms + water, levels, pH) |
An is defined by the way the living interacts with its surroundings. These surroundings are made up of two types of factors:
An is not simply a list of animals and plants; it is the functional unit created by the interaction between these biotic and . For example, in a pond , the fish (biotic) interact with the dissolved oxygen levels (abiotic) to survive. Likewise, the plants (biotic) interact with the light intensity (abiotic) to grow.
Students frequently confuse 'population' and 'community'. Remember the mnemonic: Population = Particular species; Community = Collection of species.
When defining 'population' in an exam, you must include three specific components to get full marks: same species, same area, and same time.
Edexcel marking schemes specifically look for the word 'interaction' when defining an ecosystem; always state it is the 'interaction of the community with the abiotic factors'.
Individual
A single living organism belonging to a specific species.
Species
A group of similar organisms that can interbreed to produce fertile offspring.
Habitat
The specific place or environment where an individual organism or population lives.
Population
All the organisms of the same species living in the same area at the same time.
Community
All the populations of different species living and interacting in the same area at the same time.
Ecosystem
A unit containing the community of organisms and their physical environment interacting together as a system.
Biotic factors
The living components of an ecosystem.
Abiotic factors
The non-living, physical and chemical components of an ecosystem, such as temperature, light intensity, and soil pH.
Put your knowledge into practice — try past paper questions for Biology
Individual
A single living organism belonging to a specific species.
Species
A group of similar organisms that can interbreed to produce fertile offspring.
Habitat
The specific place or environment where an individual organism or population lives.
Population
All the organisms of the same species living in the same area at the same time.
Community
All the populations of different species living and interacting in the same area at the same time.
Ecosystem
A unit containing the community of organisms and their physical environment interacting together as a system.
Biotic factors
The living components of an ecosystem.
Abiotic factors
The non-living, physical and chemical components of an ecosystem, such as temperature, light intensity, and soil pH.