Niches at HL: The idea of a niche is the same for SL and HL. You'll use it again at HL when looking at competition, invasive species and the more detailed ecosystem models.
Nothing extra here — just get the idea of a niche clear.
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Big idea: A niche is like a species’ job description — it explains how a species survives, not just where it lives.
Niche and habitat (very important!)
These two terms are often mixed up, but they mean different things.
- Habitat = its address (where it lives)
- Niche = its job (how it lives)
- Many species can share the same habitat (like many people in one city)
- But each species has its own niche (like everyone has a different job)
Habitat = address. Niche = job.
What does a niche include?
A niche includes all the ways a species uses its environment.
- Type of food eaten (e.g. owls eat mice, bees eat nectar)
- How food is obtained (e.g. hunting, grazing, filtering)
- Time of activity (e.g. night or day)
- Interactions with other species (e.g. predator, pollinator, decomposer)
- Tolerance to abiotic factors (e.g. temperature, water, light)
Example: A woodpecker’s niche: lives in forests, eats insects in tree bark, makes holes for nests, active during the day.
In exams, describe a niche using feeding role + interactions + conditions needed.
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Resource use
Species survive by using resources from their environment.
- Resources
- Different species use different resources (e.g. some birds eat seeds, others eat insects)
- Using different resources reduces competition
Different niches = less competition.
Niche overlap and competition
When species use the same resources, their niches may overlap.
- Niche overlap
- Leads to competition
- Competition can reduce population size
- One species may become less successful (or even disappear)
Example: If two types of birds eat the same seeds, they compete. If one switches to eating insects, both can survive.
Too much niche overlap = more competition.
Why niches matter in ecosystems
Niches help explain how many species can live together in the same ecosystem.
- Different niches allow species to coexist (like different jobs in a city)
- More niches usually mean higher biodiversity
- If a niche disappears, ecosystem balance can be disturbed
IB-style question — Fundamental vs realised niche + competitive exclusion
Two species of warbler, the olive warbler and the streaked warbler, both feed on insects in the same forest. The olive warbler feeds throughout the canopy and understorey. When the streaked warbler is present, the olive warbler is found only in the understorey. Distinguish between the fundamental and realised niche of the olive warbler, and explain why the change occurs. [4]
How to answer it, step by step
- Define both niches
• Fundamental niche: full range of conditions the species can use when no competitors are present (whole canopy + understorey).
• Realised niche: the actual, smaller range used when competitors are present (understorey only). - Why the niche shrinks
• Interspecific competition: streaked warbler is a more efficient forager in the upper canopy, so it competitively excludes the olive warbler from that zone.
• Both can coexist through resource partitioning — the olive warbler retreats rather than being eliminated.
Final answer
Examiners need: correct definition of both niches, interspecific competition as the cause, and competitive exclusion or resource partitioning named. Common error: saying species 'choose' different zones rather than being excluded.