Competitive exclusion and realized niches
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Question
What does the competitive exclusion principle state?
Answer
Two species **cannot occupy exactly the same niche** in the same place indefinitely — one is excluded, or they partition the resource.
Question
Define an ecological niche.
Answer
An organism's **role** in its ecosystem: the abiotic conditions it tolerates, the resources it uses and its interactions with other species.
Question
Define the fundamental niche.
Answer
The **full range** of conditions and resources a species **could** use if there were **no competitors** present.
Question
Define the realized niche.
Answer
The **smaller part** of the fundamental niche a species **actually** uses once **competition** from other species restricts it.
Question
How do the fundamental and realized niches compare in size?
Answer
The realized niche is **never larger** than the fundamental niche — competition can only restrict it.
Question
When do you see a species' fundamental niche?
Answer
When the species grows **alone**, with **no competitors** present.
Question
When do you see a species' realized niche?
Answer
When the species grows **alongside a competitor**, which squeezes it into a smaller range.
Question
What is resource partitioning?
Answer
When competing species **divide a shared resource** (by space, time or type) so each uses a different part and they can **coexist**.
Question
What are the two possible outcomes when two species compete for the same niche?
Answer
**Competitive exclusion** (one species is driven out) or **resource partitioning** (they split the resource and coexist in separate zones).
Question
Why do two competing species often occupy separate, non-overlapping zones?
Answer
Each is the **better competitor in a different part** of the gradient and **excludes** the other from the part it loses, so each is restricted to its **realized niche**.
Question
On a transect, what does a separate, non-overlapping distribution of two species suggest?
Answer
**Competition** between them — each has excluded the other from part of the gradient (competitive exclusion / partitioning).
Question
What is interspecific competition?
Answer
An interaction where two **different species** both need the **same limited resource**, so each reduces the amount available to the other.
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Ecological niches
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