1.8.6Inquiry Process
Adaptive Radiation — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 31 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 6The Process
Definition
- Definition The rapid evolution of many new species from a common ancestor, each adapted to a different niche.
Ecological opportunity
- Ecological opportunity Empty habitats, such as new islands or lands after a mass extinction, offer food and space without competitors.
Niche specialisation
- Niche specialisation Different populations exploit different resources, so natural selection favours different adaptations.
Reproductive isolation
- Reproductive isolation As the populations diverge they stop interbreeding and become separate species.
Section 2 of 6Examples
Examples
Darwin finches
- Darwin finches Around fifteen species on the Galápagos islands have beaks adapted to seeds, insects, cactus or blood.
Hawaiian honeycreepers
- Hawaiian honeycreepers Descendants of one finch ancestor now have beaks specialised for nectar, seeds and insects.
Cichlid fish
- Cichlid fish Hundreds of species in African Rift Valley lakes evolved from few ancestors, differing in jaws and diet.
Mammals
- Mammals After dinosaurs went extinct about 66 million years ago, mammals diversified into many new niches.
| Group | Place | Adaptation |
|---|---|---|
| Finches | Galápagos | Beak shape |
| Cichlids | African lakes | Jaw and teeth |
Section 3 of 6Conditions and Causes
1
A species reaches a habitat with many unoccupied niches.
2
The population grows because there is little competition or predation.
3
Variation in beak, body or behaviour lets groups use different resources.
4
Natural selection favours each specialised group in its own niche.
5
Gene flow declines and populations become distinct species.
Section 4 of 6Measuring and Explaining Radiation
Evidence from beaks
- Evidence from beaks Differences in beak depth and width match the size and hardness of the foods each finch species eats.
Key innovation
- Key innovation A new trait, such as a new jaw, can open niches that earlier forms could not use.
Convergence caution
- Convergence caution Radiations on separate islands can produce similar forms independently, such as Anolis lizards on Caribbean islands.
Mass extinction link
- Mass extinction link After extinctions, survivors diversify into the vacated niches.
Section 5 of 6Worked Example
Question
- A single species of finch colonises a remote volcanic island with no other birds.
- Explain how up to ten species might evolve there over time.
- The colonists meet many empty niches and little competition.
- Different populations specialise on different foods such as seeds, insects or nectar.
- Natural selection favours different beak sizes and shapes in each niche.
- Reproductive isolation develops between specialised groups, producing many species from one ancestor.
Answer This is adaptive radiation, the rapid diversification of one ancestral species to fill many niches.
Section 6 of 6Exam Checklist & Tips
1.8.6 – Key Points for the Exam
- Adaptive radiation Rapid diversification of a lineage into many ecological niches.
- Niche The role and position of a species in its ecosystem.
- Ecological opportunity Availability of unused resources and habitat.
- Endemic Found only in one geographical area.
Common Mistakes
- Saying that the finches deliberately changed their beaks.
- Thinking adaptive radiation needs no variation.
- Forgetting that it is usually rapid and follows empty niches.
- Confusing it with convergent evolution.
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