Realized Niche
A species may be capable of using a much broader range of resources and conditions than it actually uses in nature. That difference is the realized niche.
What Is a Niche?
A species' niche describes how it lives and uses its environment. It includes the conditions it can tolerate, the resources it uses, and its interactions with other organisms.
A habitat describes where an organism lives, while its niche describes how it lives and functions within its environment.
What Is the Realized Niche?
The realized niche is the portion of a species' potential niche that it actually occupies under real ecological conditions.
A species may be physiologically capable of surviving in a broader range of environments, but interactions with other organisms can prevent it from using all of that potential range.
Why Is the Realized Niche Often Smaller?
The environment contains more than just temperature, water, light, and other physical conditions. Organisms also interact with other organisms.
Shared Resources
Another species may use the same food, space, water, light, or other limited resource.
Predator Pressure
Predators can prevent a species from occupying locations or using resources where it would otherwise be able to survive.
Host Relationships
Parasites can negatively affect organisms and influence where or how populations occur.
Community Effects
Multiple biological interactions can combine to shape the conditions and resources a species actually uses.
Competition and the Realized Niche
Competition is one of the clearest ways to understand the difference between fundamental and realized niches.
Imagine that Species A can survive in a wide range of habitats when another species is absent. Species B, however, uses some of the same resources.
When Species B is present, Species A may be unable to use some of those resources or locations. Species A's actual range is therefore smaller than its potential range.
Other Ecological Interactions
Competition is especially important when discussing niche breadth, but other species interactions can also influence where organisms live and what resources they use.
- Predation can discourage prey from using certain habitats or resources.
- Parasitism can reduce an organism's ability to survive or reproduce.
- Mutualistic relationships can allow organisms to access resources they could not use as effectively on their own.
- Commensal relationships can provide a benefit to one species without significantly affecting another.
The realized niche therefore reflects the actual ecological conditions experienced by a population.
Fundamental Niche vs. Realized Niche
| Fundamental Niche | Realized Niche |
|---|---|
| What the species could potentially use. | What the species actually uses. |
| Describes potential conditions and resources. | Reflects real ecological conditions. |
| Does not focus on restrictions caused by biological interactions. | Includes the effects of interactions such as competition and predation. |
Realized = actual.
An Example
Imagine two bird species that feed on similar insects in a forest. Species A can tolerate a broad range of temperatures and could potentially feed throughout much of the forest.
However, Species B is a stronger competitor for insects in the coolest portions of the forest. Species A therefore uses those areas less frequently even though it can physiologically tolerate the conditions.
Common Misconceptions
Habitat describes where an organism lives. Realized niche describes the actual range of conditions and resources the organism uses.
The realized niche can be smaller because biological interactions can restrict the resources or conditions actually used.
Competition is an important example, but predation, parasitism, mutualism, and other ecological interactions can also influence a species' actual ecological range.
The realized niche describes the conditions and resources the species actually uses under the ecological conditions it experiences.
If You See This on a Test...
“The range a species actually occupies in nature”
→ Realized niche
“Competition prevents a species from using part of
its potential range”
→ The realized niche is smaller than the fundamental
niche
“A species can tolerate these conditions but does not
use them because another species is present”
→ Think realized niche
“What the species actually uses under real ecological
conditions”
→ Realized niche
Quick Practice
- Define realized niche in your own words.
- How does the realized niche differ from the fundamental niche?
- Why can competition cause the realized niche to be smaller?
- A species can tolerate a wide range of temperatures but only occupies the warmer portion of that range when another species is present. Which niche is the wider temperature range describing?
- Which niche describes what a species actually uses under real ecological conditions?
- Name one biological interaction that can influence a species' realized niche.
Key Takeaways
- A realized niche describes the conditions and resources a species actually uses.
- The realized niche can be smaller than the fundamental niche.
- Competition is an important factor that can restrict a species' actual range.
- Predation, parasitism, and other biological interactions can also influence where and how a species lives.
- The fundamental niche describes potential use, while the realized niche describes actual use.
- Remember: fundamental = could use; realized = actually uses.
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