The big idea: An organism's ecological niche is its role in an ecosystem — not just where it lives, but how it lives.
A niche is described by three things
- The abiotic conditions the species can tolerate (temperature, oxygen, pH and so on)
- Its food source (how it obtains energy)
- Its interactions with other species (predators, prey, competitors, partners)
Address and job: Think of the habitat as an organism's address, and the niche as its job.
- Ecological niche
- The role a species plays in its ecosystem — its abiotic tolerances, the way it obtains food, and its interactions with other species.
- Habitat
- The place where an organism lives. (The habitat is the 'address'; the niche is the 'job'.)
- Abiotic factor
- A non-living physical condition of the environment, such as temperature, oxygen concentration, light or pH.
- Biotic factor
- A living influence on an organism, such as predators, prey, competitors or partner species.
- Tolerance range
- The range of an abiotic factor (for example temperature) within which a species can survive and grow.
Address vs job: Two species can share the same habitat (live in the same pond) but have different niches — one feeds on algae at the surface, the other on insects near the bottom.
So 'where it lives' alone never fully describes a niche; you must also say what it eats and how it interacts with other species.
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To describe a species' niche fully you give three kinds of information: the physical conditions it can tolerate, its food source, and its interactions with other species.
Together these define exactly how the species fits into its ecosystem.
| Part of the niche | What it describes | Example for a small lake fish |
|---|---|---|
| Abiotic tolerances | The range of physical conditions the species can survive in (temperature, oxygen, pH, light) | Survives in cool, well-oxygenated, shallow water |
| Food / energy source | How and what the species feeds on (its mode of nutrition) | Eats small invertebrates among the plants |
| Interactions with other species | How it relates to predators, prey, competitors and partners | Shelters among submerged plants to avoid predators |
Abiotic tolerances set the limits: Every species can only survive within a tolerance range for each abiotic factor. A fish that needs cool, well-oxygenated water cannot live in a warm, stagnant pond — the conditions fall outside its tolerance.
Tolerances as data: These tolerance ranges are a big part of the niche, and exams often give them as data (for example a table of preferred temperatures) and ask you to reason about which species could live where.
Fundamental vs realized niche: The fundamental niche is the full range of conditions and resources a species could use if nothing got in its way. The realized niche is the smaller part it actually uses once competitors are present.
Competition shrinks the niche: When two species want the same resources, competition pushes each into a smaller realized niche — this is the start of the competitive exclusion idea you meet in 2.10.4.
A niche is a species' role and its place along a resource gradient. Alone, species A occupies its full fundamental niche; a competitor restricts it to a smaller realized niche.
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Fundamental niche
- The full range a species could occupy
- Assumes no competitors
- The species' potential
- Larger than the realized niche
Realized niche
- The part it actually occupies
- Takes competitors into account
- What the species really does
- Smaller — restricted by competition
An easy way to remember: Fundamental = the full menu a species could order from. Realized = what's left on the plate after competitors have taken their share.
And for the three parts of a niche: conditions, food, friends-and-foes (abiotic tolerances, food source, interactions).
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The big idea: A niche is made of interactions: with abiotic conditions and with other organisms. Each one affects the species' growth, survival or reproduction.
The points to remember
- Abiotic interactions: the conditions it needs, such as temperature, oxygen, light or water.
- How it obtains food: what it eats, or how it makes its own food.
- Biotic interactions: predators, prey, competitors, parasites and partners.
- What it needs to reproduce, such as nest sites or breeding grounds.
Remember it as: Ask: what does it need, what does it eat, who eats it, who competes with it, where does it breed?
Real example: the Atlantic puffin. Puffins feed their chicks on sandeels, nest in burrows on grassy cliff tops and are hunted by great skuas; in years when sandeels are scarce, many chicks starve: food is part of the niche.
Trap: 'It lives in a river' describes the habitat. A niche answer must say how it lives there.
How this is tested: Three question types come up on the niche, each answered in its own way.
| Question | What it asks | How to score |
|---|---|---|
| Short Define or Outline | What an ecological niche is | Give more than just 'where it lives': include the abiotic tolerances, the food source and the interactions with other species |
| Data question (a favourite) | The preferred temperature ranges (or oxygen needs) of several species; deduce which statements about their niches are valid | Read the data, do not rely on memory |
| Suggest | Why an organism is more abundant in one micro-habitat than another | Link your answer to the niche (the shelter, food or conditions that place provides) |
Exam-style question — define an ecological niche
Define the term ecological niche. [3]
How to score all three marks
- Start with the role. A niche is the role a species plays in its ecosystem — how it lives, not only where.
- Name the abiotic part. It includes the range of abiotic conditions (such as temperature and oxygen) that the species can tolerate.
- Add food and interactions. It also includes the species' food/energy source (mode of nutrition) and its interactions with other species (predators, prey, competitors).
Final answer
An ecological niche is the role a species plays in its ecosystem: the range of abiotic conditions it tolerates, the way it obtains food, and its interactions with other species.
Why this works: It does not stop at 'where the organism lives'. It names all three parts — abiotic tolerances, food source and interactions — so each is a separate scoring point.
The single most common error is answering only with the habitat ('it lives in a lake').
| Part of the niche | What it describes | Example for a small lake fish |
|---|---|---|
| Abiotic tolerances | The range of physical conditions the species can survive in (temperature, oxygen, pH, light) | Survives in cool, well-oxygenated, shallow water |
| Food / energy source | How and what the species feeds on (its mode of nutrition) | Eats small invertebrates among the plants |
| Interactions with other species | How it relates to predators, prey, competitors and partners | Shelters among submerged plants to avoid predators |