What is an ecological niche?

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), and its interactions with other species (predators, prey, competitors, partners).

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.

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.

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.

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.

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 memory hook: 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).

How this is tested: A short Define or Outline question asks what an ecological niche is — score by giving more than just 'where it lives': include the abiotic tolerances, the food source and the interactions with other species.

A favourite Paper 1B data format gives the preferred temperature ranges (or oxygen needs) of several species and asks you to deduce which statements about their niches are valid — read the data, do not rely on memory.

A Suggest question may ask 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).

✓ Why this scores full marks: 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').