Definition
Niche
A niche describes the role of a species in its environment, including how it interacts with biotic (living) and abiotic (non-living) factors.
- A niche refers to the ecological role of a species within an ecosystem — how it interacts with both biotic (living) and abiotic (non-living) factors.
- It includes everything that affects the species’ survival and reproduction: habitat, food sources, competition, predators, and environmental conditions.
Fundamental Niche
Definition
Fundamental niche
The fundamental niche is the full range of conditions and resources a species could theoretically use if there were no competition, predators, or other limiting factors.
- The fundamental niche represents the potential ecological space a species could occupy if there were no competitors, predators, or limiting factors.
- It is determined by the species’ physiological tolerance to environmental conditions and the availability of essential resources.
- It is theoretical, describing where a species could live, not necessarily where it does live.
Realized Niche
Definition
Realized niche
A realized niche is the actual conditions in which a species exists due to competition, predation, and environmental constraints.
- The realized niche represents the actual conditions under which a species exists, given biotic interactions (competition, predation, mutualism).
- It is always narrower than the fundamental niche, as species are restricted by the presence of other organisms.
- It results from adaptations and competitive interactions that determine the actual space and resources a species uses.
Analogy
- Think of the fundamental niche as a dream apartment, where you could live if money (competition) wasn’t an issue.
- The realized niche is the actual apartment you can afford, considering your budget (biotic limits).
Case study
Joseph Connell’s Study of Barnacle Species
- Location: Rocky shores of the UK
- Species Studied:
- Chthamalus stellatus (small barnacle)
- Semibalanus balanoides (larger barnacle)
Background
- Both species live in the intertidal zone (area exposed between high and low tide).
- Connell observed that:
- Chthamalus dominated the upper intertidal zone.
- Semibalanus dominated the middle and lower intertidal zones.
Connell’s Experiments
- Removing Chthamalus from Upper Zones
- Semibalanus did not move into the upper zone.
- Interpretation: Semibalanus couldn’t tolerate drying conditions (desiccation).
- Therefore, Semibalanus’s fundamental niche = realized niche (both restricted to middle and lower zones).
- Removing Semibalanus from Middle Zones
- Chthamalus expanded downward into the middle zone.
- Interpretation: Chthamalus was outcompeted by Semibalanus for space in this region.
- Therefore, Chthamalus’s realized niche (upper zone only) is smaller than its fundamental niche (upper + middle zones).
Conclusion
- Competition (biotic factor) limits Chthamalus to a smaller realized niche.
- Physiological tolerance (abiotic factor) limits Semibalanus to a narrower vertical range.
Case study
Brown and Green Anole Lizards
- Location: Caribbean Islands and Southern United States
- Species Studied:
- Anolis carolinensis (green anole)
- Anolis sagrei (brown anole)
Background
- Both species occupy similar habitats and compete for space, food, and sunlight.
- When found together:
- The brown anole dominates lower vegetation (closer to ground).
- The green anole is restricted to higher branches.
Interpretation
- Fundamental Niche: Both species could theoretically occupy all levels of vegetation.
- Realized Niche: Due to competitive exclusion, green anoles shift upward and occupy higher zones.
- This spatial separation is a form of niche partitioning, reducing direct competition.
Ecological Significance
- Differentiating between fundamental and realized niches is essential to:
- Understand species distribution and biodiversity patterns.
- Predict responses to environmental changes (e.g., climate shifts).
- Design effective conservation strategies by identifying critical habitat needs.
- It helps ecologists understand how competition regulates community structure and maintains ecological balance
Exam technique
- Questions may ask for examples showing how the realized niche is smaller than the fundamental niche.
- Mention Connell’s barnacles or Caribbean anoles and explain the mechanism (competition).
Self review
- Define fundamental niche and realized niche.
- How does interspecific competition influence realized niches?
- Explain Connell’s barnacle experiment and its significance for niche theory.
- Describe how the green and brown anole lizards demonstrate resource partitioning.
