2.9.5Additional lessons
Competition Between Species — IB Biology SL Revision Notes & Topical Questions
5 min read 6 parts Lesson 49 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.
Section 1 of 6Types of Competition
Interspecific
- Interspecific Competition between individuals of different species for the same limited resource.
Intraspecific
- Intraspecific Competition between individuals of the same species, which share exactly the same needs.
Resources
- Resources Plants compete for light, water and nutrients, while animals compete for food, shelter and mates.
Effect
- Effect The competitor that uses the resource more efficiently gains more and its population may increase.
Population control
- Population control Competition limits population size and so helps to keep populations within carrying capacity.
Section 2 of 6Niches
Niches
Niche
- Niche The role of a species in its habitat, including its food, habitat, activity time and interactions.
Fundamental niche
- Fundamental niche The full range of conditions and resources a species could use if there were no competitors.
Realised niche
- Realised niche The narrower range actually used because of competition and other biotic interactions.
Resource partitioning
- Resource partitioning Species divide a resource by feeding at different times or places, reducing competition.
Section 3 of 6Competitive Exclusion
1
Two species with identical niches compete directly for the same resources.
2
Even a small advantage lets one species grow faster and use more of the resource.
3
The population of the weaker competitor falls until it is excluded from that habitat.
4
Experiments with two Paramecium species grown together showed one species surviving while the other declined.
5
Coexistence is possible only if the niches differ enough to reduce competition.
Section 4 of 6Examples
Examples
Barnacles
- Barnacles On a rocky shore Balanus outcompetes Chthamalus on the lower shore, so Chthamalus is restricted to the higher shore.
Plants
- Plants Tall trees shade smaller plants, which then compete for light and may be restricted to open areas.
Squirrels
- Squirrels Introduced grey squirrels have contributed to the decline of red squirrels in parts of Britain, partly through competition for food.
Section 5 of 6Competition and Populations
Competition and Populations
Density-dependent
- Density-dependent Competition becomes stronger as population density rises, because resources are shared among more individuals.
Winners
- Winners The species that is better adapted to the shared resource increases in number.
Coexistence
- Coexistence Different niches allow similar species to live together in the same habitat.
Section 6 of 6Exam Checklist & Tips
2.9.5 – Key Points for the Exam
- Interspecific competition Competition between members of different species.
- Intraspecific competition Competition between members of the same species.
- Competitive exclusion The idea that two species cannot occupy the same niche indefinitely.
- Realised niche The niche a species actually occupies in the presence of competitors.
Common Mistakes
- Mixing up intra and interspecific competition; intra means within one species.
- Saying that competition always kills the weaker species at once, when it may only reduce its numbers or range.
- Assuming that the realised niche is larger than the fundamental niche.
- Forgetting that competition may be for non-food resources such as light, space or nesting sites.
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