3.7.8Additional lessons
Interspecific Competition — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 89 of 142
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.
Part 1 of 5Niches and Competition
Competition between species can change where each one lives.
Niche
- Niche The role of a species in its habitat, including its use of resources and its interactions with other species.
Similar niches
- Similar niches If two species have very similar niches they compete for the same resources.
Outcome
- Outcome One species is usually better adapted and outcompetes the other.
Competitive exclusion
- Competitive exclusion The weaker species is forced out of part of its range or becomes locally extinct.
Part 2 of 5Fundamental and Realised Niche
Fundamental and Realised Niche
Fundamental niche
- Fundamental niche The full range of conditions and resources a species could use in the absence of competitors.
Realised niche
- Realised niche The narrower range that a species actually occupies because of competition and other interactions.
Shift
- Shift When a competitor is present, the weaker species is limited to its realised niche.
Evidence
- Evidence If the competitor is removed, the weaker species may expand into its fundamental niche.
| Niche | Competitors | Range of use |
|---|---|---|
| Fundamental | Absent | Wider |
| Realised | Present | Narrower |
Part 3 of 5Testing for Competition
1
Make a hypothesis, for example that species A excludes species B from part of a habitat.
2
Sample both species using random quadrats and record presence or absence at each location.
3
Remove one species from a small area and keep a control area where it is not removed.
4
Measure the distribution of the second species in both areas.
5
If the second species spreads into the cleared area, competition is likely, but this does not prove it.
Part 4 of 5Experiments and Observations
Laboratory
- Laboratory Conditions are controlled and only the independent variable changes, such as culturing two bacterial species separately and together.
Field
- Field Results are closer to real conditions but many variables cannot be controlled.
Observation
- Observation Observing natural distributions can suggest hypotheses, while experiments test them.
Limitation
- Limitation Laboratory results cannot be directly applied to real ecosystems.
Part 5 of 5Exam Checklist & Tips
3.7.8 – Key Points for the Exam
- Niche The role of a species in an ecosystem.
- Competitive exclusion The exclusion of one species from a niche by a better competitor.
- Fundamental niche The potential niche in the absence of competition.
- Realised niche The niche actually occupied.
Common Mistakes
- Using niche to mean only the place where a species lives.
- Saying two species with identical niches can usually coexist.
- Treating removal experiments as proof of competition.
- Confusing fundamental and realised niche.
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