What causes extinction, and how does it shape the diversity of life?
Topic 7.11 Extinction: explain the causes of extinction, including mass extinctions, and its role in shaping biodiversity.
A focused answer to AP Biology Topic 7.11, covering the causes of extinction, background versus mass extinction, the five mass extinctions, adaptive radiation after extinction, and the current human-driven loss, with a worked example.
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What this topic is asking
The College Board (Topic 7.11) wants you to explain the causes of extinction, distinguish background from mass extinction, and describe how extinction (and the adaptive radiation that can follow) shapes biodiversity.
Causes of extinction
Background and mass extinction
Adaptive radiation after extinction
The current, human-driven rise in extinction rates is concerning precisely because it is fast: species are being lost far quicker than new ones evolve, and habitat destruction removes the niches that diversification would need. This links extinction directly to the disruptions-to-ecosystems and biodiversity topics in Unit 8.
Try this
Q1. State why low genetic diversity increases extinction risk. [1 point]
- Cue. Few variants mean a lower chance that any individuals are suited to new conditions, so the species is less able to adapt to change.
Q2. Explain how a mass extinction can lead to greater diversity afterwards. [2 points]
- Cue. It empties many niches; surviving lineages diversify rapidly into the available niches (adaptive radiation), producing many new species over time.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2020 (style)3 marksSection II (short FRQ). (a) Explain how a rapid environmental change can cause a species to go extinct. (b) Explain how a mass extinction can lead to an increase in diversity afterwards through adaptive radiation.Show worked answer →
A 3-point explain FRQ on extinction and its aftermath.
(a) Explain (2 points): (1 point) if the environment changes faster than a population can adapt, and no existing variants are suited to the new conditions; (1 point) the whole population fails to survive and reproduce, so the species goes extinct (low genetic diversity makes this more likely).
(b) Explain (1 point): a mass extinction empties many niches, so surviving lineages diversify rapidly into the available niches (adaptive radiation), producing many new species over time.
Markers reward linking the rate of environmental change to extinction risk and explaining adaptive radiation into vacated niches.
AP 2017 (style)1 marksSection I (multiple choice). A species with very low genetic diversity is more likely to go extinct when the environment changes because: (A) it reproduces too quickly. (B) it lacks the variation needed for some individuals to survive the new conditions. (C) it has too many mutations. (D) it cannot undergo mitosis.Show worked answer →
The correct answer is (B).
Low genetic diversity means few variants, so it is less likely that any individuals happen to be suited to new conditions; if none can survive and reproduce, the species goes extinct. High diversity raises the chance some individuals survive environmental change.
Related dot points
- Topic 7.10 Speciation: explain how reproductive isolation leads to speciation, including allopatric and sympatric speciation.
A focused answer to AP Biology Topic 7.10, covering the biological species concept, reproductive isolation (prezygotic and postzygotic barriers), allopatric and sympatric speciation, and rates of speciation, with a worked example.
- Topic 7.12 Variations in Populations: explain why genetic variation within a population is important for survival and the response to environmental change.
A focused answer to AP Biology Topic 7.12, covering the sources and importance of genetic diversity, how variation buffers populations against change, the risks of low diversity, and the role of variation in evolution, with a worked example.
- Topic 7.1 Introduction to Natural Selection: explain the conditions required for natural selection and how it leads to changes in a population.
A focused answer to AP Biology Topic 7.1, covering Darwin's reasoning, the conditions for natural selection (variation, heritability, overproduction, differential reproduction), fitness, and how selection changes allele frequencies, with a worked example.
- Topic 8.7 Disruptions to Ecosystems: explain how natural and human-caused disruptions affect ecosystems and how ecosystems respond.
A focused answer to AP Biology Topic 8.7, covering natural and human disturbances, invasive species, habitat loss, climate change, ecological succession, and how ecosystems respond and recover, with a worked example.
- Topic 8.6 Biodiversity: explain how biodiversity contributes to ecosystem stability and resilience.
A focused answer to AP Biology Topic 8.6, covering species and genetic diversity, how diversity supports ecosystem stability and resilience, the effects of low diversity, and a worked example using a diversity comparison.
Sources & how we know this
- AP Biology Course and Exam Description — College Board (2020)