Competitive exclusion, niche & allelopathy
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Question
What is an ecological niche?
Answer
The **full role** of a species in its community — its abiotic tolerances, the resources it uses, and its interactions with other species.
Question
State the competitive exclusion principle.
Answer
Two species that need the **same limited resource** cannot coexist **indefinitely**; the better competitor excludes the other.
Question
What happens to the species that loses in competitive exclusion?
Answer
It is **excluded** — it dies out locally, or survives only by shifting to a **different niche** (using a different resource).
Question
What is a fundamental niche?
Answer
The **whole niche** a species could occupy if **no competitors** were present.
Question
What is a realized niche?
Answer
The **smaller** part of the niche a species **actually** occupies once competitors restrict it.
Question
How does competition change a species' niche?
Answer
It shrinks the **fundamental niche** down to a smaller **realized niche**.
Question
What is allelopathy?
Answer
When a **plant releases a chemical** that **inhibits the growth/germination of other plants** nearby, reducing competition.
Question
What is antibiosis?
Answer
When a **microorganism releases a chemical** that **inhibits the growth of other microorganisms**, reducing competition.
Question
Give an example of allelopathy.
Answer
The **black walnut** tree releases a chemical into the soil that stops many plants growing beneath it.
Question
How can you tell allelopathy from antibiosis?
Answer
**Allelopathy** = a **plant** inhibits other **plants**; **antibiosis** = a **microbe** inhibits other **microbes**. Both are chemical competition.
Question
If a population crashes only when grown WITH another species, what is the likely cause?
Answer
**Interspecific competition** leading to **competitive exclusion** — not predation or disease.
Question
Why can two species sometimes coexist despite competing?
Answer
If their niches **overlap only partly**, they can use slightly different resources and avoid full competitive exclusion.
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Topic 3.8 hub
Populations and communities
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