4.12.5Theme D — Continuity and change
Climate Change: Evolution — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 18 of 18 Unit quiz
Part 1 of 5Climate as a Selection Pressure
Changing climate alters which phenotypes survive, so allele frequencies shift.
Heat tolerance
- Individuals with alleles that give resistance to high temperature survive hot spells and leave more offspring.
Timing alleles
- Alleles that cause earlier breeding or flowering are favoured if the season starts sooner.
Drought tolerance
- Plants with deep roots or water-saving leaves have an advantage in drier habitats.
Heritable variation
- Selection works only where such differences are inherited and already present in the population.
| Factor | Effect on speed of adaptation |
|---|---|
| Short generation time | Faster |
| High genetic variation | Faster |
| Large population | More variants available |
| Small isolated population | Slower or extinction |
Part 2 of 5Possible Outcomes for a Population
1
The climate changes faster than before, producing a new set of selection pressures on a population.
2
Some individuals carry alleles that give a better fit to the new conditions, such as heat tolerance.
3
These individuals reproduce more successfully, and the allele frequency of the favourable alleles rises each generation.
4
If adaptation is fast enough the population persists, otherwise it shrinks, moves to a new area or becomes extinct.
Part 3 of 5Who Adapts Best?
Who Adapts Best?
Fast breeders
- Insects and microbes with many generations per year can show evolutionary change in a few years.
Slow breeders
- Long-lived trees and large mammals have long generation times, so they adapt much more slowly than the climate changes.
Dispersal
- Species that can move to cooler regions may avoid the need to adapt, if habitat is connected.
Conservation
- Maintaining genetic diversity within populations helps retain the variation needed for future adaptation.
Part 4 of 5Worked Example
Question
- The frequency of an early-flowering allele rises from 0.30 to 0.45 over 15 generations in an annual plant.
- Calculate the mean change per generation, and the number of years if the plant has one generation a year.
- Change = 0.45 − 0.30 = 0.15.
- Mean change per generation = 0.15 ÷ 15 = 0.01.
- One generation per year means the change took 15 years.
Answer 0.01 per generation, over 15 years
Part 5 of 5Exam Checklist & Tips
4.12.5 – Key Points for the Exam
- Selection pressure An environmental factor that influences survival and reproduction.
- Genetic variation Differences in alleles between individuals in a population.
- Generation time The average time between birth of parents and birth of offspring.
- Adaptation A heritable feature that improves fitness in a given environment.
- Extinction Complete loss of a species.
Common Mistakes
- Writing that individuals change their genes in response to the climate.
- Assuming all species evolve fast enough to survive rapid climate change.
- Forgetting that a population needs existing genetic variation for selection to act.
- Mixing up acclimatisation, which is a non-heritable change, with evolution.
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