2.10.5Inquiry Process
Competition Between Species — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 100 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Fundamental and Realised Niches
The niche of a species can be considered with or without the effects of other species.
Niche
- Niche The role of a species in its habitat, including what it eats, what eats it, and the abiotic conditions it uses.
Fundamental niche
- Fundamental niche The full range of conditions and resources in which a species could survive and reproduce without other species present.
Realised niche
- Realised niche The smaller range a species actually occupies once competition and predation limit it.
Relationship
- Relationship The realised niche is always the same size as or smaller than the fundamental niche.
| Feature | Fundamental niche | Realised niche |
|---|---|---|
| Limited by | Abiotic tolerance only | Abiotic factors and biotic interactions |
| Size | Larger | Smaller or equal |
| Competition | Absent | Present |
Section 2 of 5Barnacle Case Study
1
Chthamalus can live over a wide band of rocky shore, so its fundamental niche is large.
2
Balanus competes strongly for space on the lower shore and excludes Chthamalus there.
3
Chthamalus therefore survives only higher on the shore where it is exposed to air for longer.
4
Balanus cannot tolerate the drying conditions of the upper shore, so it stays lower.
5
The realised niche of Chthamalus is thus much smaller than its fundamental niche.
Section 3 of 5Competitive Exclusion
Competitive Exclusion
Principle
- Principle Two species cannot occupy exactly the same niche indefinitely;
- the better competitor eventually excludes the other.
Outcomes
- Outcomes The weaker species may be forced into a different niche, restricted to a smaller area, or become locally extinct.
Paramecium
- Paramecium Grown alone, P. aurelia and P. caudatum both thrive, but together P. aurelia outcompetes P. caudatum.
Laboratory caution
- Laboratory caution Such experiments use controlled conditions, whereas in nature species rarely share identical niches.
Section 4 of 5Reducing Competition
Resource partitioning
- Resource partitioning Species with similar needs divide a resource, for example warblers feeding in different parts of the same trees.
Different timing
- Different timing Species may feed at different times of day, as with diurnal and nocturnal predators.
Different foods
- Different foods Slight differences in diet or feeding method reduce overlap between species.
Result
- Result Partitioning allows coexistence and increases the number of species in a community.
Section 5 of 5Exam Checklist & Tips
2.10.5 – Key Points for the Exam
- Niche The role of a species in its habitat, including its use of resources and its interactions.
- Fundamental niche The potential range of conditions and resources a species could use.
- Realised niche The actual range a species uses after biotic interactions are taken into account.
- Competitive exclusion The elimination of one species from a niche by a better competitor.
- Resource partitioning Division of resources among species so they can coexist.
Common Mistakes
- Saying fundamental niche is larger because of competition; competition shrinks the realised niche.
- Describing niche as the place where an organism lives; that is the habitat.
- Concluding the lab Paramecium result always happens in nature.
- Forgetting that the outcome can be niche shift as well as extinction.
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