Why is biodiversity important for the health and stability of ecosystems?
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.
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What this topic is asking
The College Board (Topic 8.6) wants you to explain how biodiversity (species and genetic diversity) contributes to ecosystem stability and resilience, and why low diversity makes ecosystems more vulnerable.
What biodiversity is
Diversity, stability and resilience
Why low diversity is risky
Monoculture crops illustrate the danger: a field of one genetically uniform variety can be wiped out by a single pest or disease, because all the plants share the same vulnerabilities. This links biodiversity to the value of genetic variation within populations (Unit 7) and to the consequences of the disruptions covered in the next topic, where human activity is the main driver of biodiversity loss.
Try this
Q1. State two levels of biodiversity. [2 points]
- Cue. Species diversity (the variety of species in an area) and genetic diversity (the variation in alleles within a species).
Q2. Explain why high biodiversity makes an ecosystem more resilient to disturbance. [2 points]
- Cue. More species provide functional redundancy, so if some are lost others can fill their roles, and a wider range of species gives more ways to respond to change, helping the ecosystem keep functioning and recover.
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 2021 (style)4 marksSection II (long FRQ excerpt). Two ecosystems experience the same disturbance: ecosystem A has high species diversity, ecosystem B has low species diversity. (a) Predict which ecosystem is more likely to recover and explain why. (b) Explain how genetic diversity within a species also contributes to ecosystem stability.Show worked answer →
A 4-point predict-and-explain FRQ on biodiversity.
(a) Predict and explain (2 points): (1 point) ecosystem A (high diversity) is more likely to recover and remain stable; (1 point) because more species means more functional redundancy, so if some are lost others can fill their roles, keeping the ecosystem functioning.
(b) Explain (2 points): (1 point) genetic diversity within a species means some individuals are more likely to survive a disturbance such as disease; (1 point) so the species persists and continues its role, supporting overall ecosystem stability.
Markers reward predicting the diverse ecosystem recovers and linking both species diversity (functional redundancy) and genetic diversity to stability.
AP 2017 (style)1 marksSection I (multiple choice). An ecosystem with high biodiversity is generally: (A) less stable and less resilient. (B) more stable and more resilient to disturbance. (C) unable to recover from disturbance. (D) identical in function to a low-diversity ecosystem.Show worked answer →
The correct answer is (B).
Higher biodiversity generally makes an ecosystem more stable and more resilient, because more species provide functional redundancy and a greater range of responses to disturbance, so the ecosystem is more likely to keep functioning and to recover.
Related dot points
- Topic 8.5 Community Ecology: explain the types of interactions between species in a community and their effects on the species involved.
A focused answer to AP Biology Topic 8.5, covering competition, predation, the niche, symbiosis (mutualism, commensalism, parasitism), keystone species and trophic relationships, with a worked interaction 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 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 8.2 Energy Flow Through Ecosystems: explain how energy flows through trophic levels and why energy is lost between levels.
A focused answer to AP Biology Topic 8.2, covering trophic levels, food chains and webs, the 10 percent rule, energy pyramids, productivity, and why energy decreases up the chain, with a worked energy-transfer calculation.
- 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.
Sources & how we know this
- AP Biology Course and Exam Description — College Board (2020)