Identify the type of biodiversity
Species, genetic, or ecosystem diversity.
How does biodiversity affect ecosystem stability in AP Biology?
Biodiversity and ecosystem stability AP Biology connects variety of life to how ecosystems respond to change. Biodiversity can increase ecosystem stability because diverse ecosystems often contain more species, more genetic variation, and more functional roles. This can help ecosystems resist disturbance, recover after disturbance, and maintain food web function.
Short answer
More biodiversity often means more stability because the ecosystem has more functional backup.
Biodiversity and Ecosystem Stability Key Takeaways
- Biodiversity includes species diversity, genetic diversity, and ecosystem diversity.
- Species richness is the number of species in a community.
- Species diversity includes both species number and relative abundance.
- Higher biodiversity can increase resilience after disturbance.
- Higher biodiversity can increase resistance to some changes.
- Invasive species, habitat loss, and disturbance can reduce biodiversity and stability.
Biodiversity and Stability AP Shortcut
Compact reference
- Species richness = number of species.
- Species diversity = richness plus relative abundance.
- Genetic diversity = variation within a species.
- Resistance = withstand disturbance.
- Resilience = recover after disturbance.
- Functional redundancy = backup ecological roles.
- Keystone species can maintain diversity.
- Invasive species can reduce native biodiversity.
AP exam clue: On FRQs, explain the mechanism: more biodiversity can provide functional redundancy and alternative food web pathways.
Biodiversity and Stability Reasoning Ladder
Read the community data
Look for species count, relative abundance, or change over time.
Identify the disturbance
Fire, drought, invasive species, disease, habitat loss, or species removal.
Predict stability effect
Will the ecosystem resist change or recover after change?
Explain the mechanism
Use redundancy, food web alternatives, genetic variation, or niche roles.
Connect to AP claim
Use evidence to support how biodiversity affects stability.
AP exam clue: Do not only say "biodiversity increases stability." Explain why the ecosystem is more resistant or resilient.
What is biodiversity?
Direct answer: Biodiversity is the variety of life in an area, including species diversity, genetic diversity, and ecosystem diversity.
- Biodiversity can be measured at different levels.
- High biodiversity usually means more biological variety.
- Biodiversity can affect food webs, resilience, and ecosystem function.
- AP Biology often asks students to connect biodiversity to stability or disturbance recovery.
Course context: AP Biology and Unit 8 Ecology. See also responses to the environment when organisms face changing conditions.
What is species richness?
Direct answer: Species richness is the number of different species in a community.
- Richness counts how many species are present.
- It does not describe how common each species is.
- Two communities can have the same richness but different diversity.
- AP questions may ask students to compare species counts.
What is species diversity?
Direct answer: Species diversity includes both the number of species and their relative abundance.
- Species diversity includes richness.
- Species diversity also considers evenness.
- A community dominated by one species may have lower diversity.
- More even communities usually have higher species diversity.
Species Richness vs Species Diversity
Direct answer: Species richness counts species, while species diversity considers both species count and how evenly individuals are distributed among species.
| Feature | Species Richness | Species Diversity |
|---|---|---|
| Meaning | Number of species in a community | Species number plus relative abundance |
| Uses abundance? | No — counts species only | Yes — considers how common each species is |
| What it measures | How many species exist | How evenly species are represented |
| AP exam clue | Species count given | One species dominates despite high count |
| Example | 18 plant species in a grassland | 18 species but one makes up 80% of individuals |
What is genetic diversity?
Direct answer: Genetic diversity is the amount of genetic variation within a population or species.
- Genetic diversity can help populations respond to environmental change.
- Low genetic diversity can increase vulnerability to disease or disturbance.
- Genetic diversity connects ecology to evolution.
- AP Biology may link genetic variation to survival and adaptation.
What is ecosystem diversity?
Direct answer: Ecosystem diversity is the variety of ecosystems or habitats in a region.
- Different ecosystems support different species.
- Habitat variety can increase regional biodiversity.
- Ecosystem diversity can provide more ecological roles and interactions.
- Habitat loss can reduce ecosystem diversity.
What is ecosystem stability?
Direct answer: Ecosystem stability is the ability of an ecosystem to maintain function during disturbance or recover after disturbance.
- Stability can involve resistance.
- Stability can involve resilience.
- Stable ecosystems maintain energy flow, nutrient cycling, and community structure.
- Biodiversity can support stability by providing backup roles.
What is resistance in ecology?
Direct answer: Resistance is the ability of an ecosystem to withstand disturbance without major change.
- A diverse plant community losing little biomass during drought.
- A food web maintaining function after one prey species declines.
- A community with multiple species filling similar roles.
AP clue: Resistance means the ecosystem changes less during the disturbance.
What is resilience in ecology?
Direct answer: Resilience is the ability of an ecosystem to recover after disturbance.
- A forest regrowing after fire.
- A grassland recovering after drought.
- A food web returning to similar structure after population decline.
AP clue: Resilience means the ecosystem rebounds after being disturbed.
Resistance vs Resilience
Direct answer: Resistance describes how much an ecosystem changes during disturbance, while resilience describes how well it recovers afterward.
| Feature | Resistance | Resilience |
|---|---|---|
| Meaning | Withstand disturbance without major change | Recover after disturbance |
| Timing | During the disturbance | After the disturbance |
| Graph pattern | Ecosystem function stays relatively stable | Ecosystem drops then returns toward original function |
| AP clue | Little change during drought or fire | Biomass or structure returns within a few years |
| Example | Diverse plant community loses little biomass during drought | Forest regrows after fire |
Why does biodiversity increase ecosystem stability?
Direct answer: Biodiversity can increase ecosystem stability because different species may perform similar roles, use different resources, or respond differently to disturbances.
- Functional redundancy provides backup if one species declines.
- Alternative food sources can stabilize food webs.
- Genetic diversity can increase survival under changing conditions.
- Diverse communities may recover faster after disturbance.
Population context: population ecology and population growth models help explain how individual species change before community-level stability shifts.
What is functional redundancy?
Direct answer: Functional redundancy occurs when multiple species perform similar ecological roles.
- Redundancy provides backup roles.
- If one species declines, another may partly replace its function.
- Redundancy can support resilience.
- AP questions may ask why diverse ecosystems recover better.
How do keystone species affect biodiversity?
Direct answer: Keystone species can help maintain biodiversity because they have disproportionately large effects on community structure.
- Removing a keystone species can reduce diversity.
- Keystone predators can prevent one species from dominating.
- Keystone species can shape food webs and community balance.
How do invasive species affect biodiversity?
Direct answer: Invasive species can reduce biodiversity by competing with native species, changing food webs, or altering habitat conditions.
- Invasive species may lack natural predators.
- They can outcompete native species for resources.
- They can reduce species richness or evenness.
- Biodiversity loss can reduce ecosystem stability.
How does disturbance affect ecosystem stability?
Direct answer: Disturbance can reduce ecosystem stability by changing species abundance, removing habitat, disrupting food webs, or lowering biodiversity.
- Disturbance can include fire, drought, flood, disease, or human activity.
- Some ecosystems recover quickly.
- Recovery depends on biodiversity, soil, seed banks, climate, and species interactions.
- Disturbance connects biodiversity to succession.
Study Ecological Succession → · density-dependent and density-independent factors
How does biodiversity affect food web stability?
Direct answer: Biodiversity can stabilize food webs by providing multiple feeding pathways and alternative energy routes.
- If one prey species declines, predators may use other prey.
- If one producer declines, consumers may rely on other producers.
- More connected food webs can sometimes buffer change.
- Simplified food webs can be more vulnerable to species loss.
AP Biology Data Patterns for Biodiversity and Stability
Data pattern: More species and more even abundance.
What to do: Identify higher species diversity.
Data pattern: Same species count but one species dominates.
What to do: Explain lower evenness and lower diversity.
Data pattern: Ecosystem changes little during disturbance.
What to do: Identify resistance.
Data pattern: Ecosystem drops after disturbance but returns to original function.
What to do: Identify resilience.
Data pattern: Invasive species increases while native species decline.
What to do: Explain biodiversity loss and reduced stability.
Data pattern: Removing one species causes large community change.
What to do: Consider a keystone species effect.
Quick Check
Quick Check
Test yourself in 5 seconds
Two ecosystems have the same number of species. Ecosystem A has similar numbers of individuals in each species, while Ecosystem B is dominated by one species. Which ecosystem has higher species diversity?
Answer: A — Ecosystem A has higher species diversity because species diversity includes both species richness and relative abundance, or evenness.
Common Biodiversity and Stability Mistakes
Mistake: Thinking richness and diversity are identical.
Fix: Richness counts species; diversity also includes relative abundance.
Mistake: Saying biodiversity always prevents disturbance.
Fix: Biodiversity can improve resistance or resilience, but disturbances can still happen.
Mistake: Confusing resistance and resilience.
Fix: Resistance means withstand change; resilience means recover after change.
Mistake: Ignoring genetic diversity.
Fix: Genetic diversity can help populations respond to environmental change.
Mistake: Assuming invasive species increase stability because they add species.
Fix: Invasive species often reduce native biodiversity and disrupt food webs.
Mistake: Saying a keystone species is just the most abundant species.
Fix: Keystone species have large effects relative to abundance.
Biodiversity and Ecosystem Stability FRQ Strategy
Direct answer: For biodiversity and stability FRQs, identify the biodiversity measure, use data from the prompt, explain the effect on resistance or resilience, and connect the pattern to food webs, redundancy, genetic variation, or species interactions.
The data show ____ biodiversity because ____. This affects ecosystem stability by ____. The ecosystem may be more resistant/resilient because ____.
Scoring checklist
- Identifies biodiversity measure.
- Uses evidence from the data.
- Distinguishes richness, diversity, resistance, or resilience correctly.
- Explains a mechanism such as redundancy, alternative food webs, or genetic variation.
- Connects biodiversity to stability or recovery.
- Avoids vague "biodiversity is good" statements.
More practice: Unit 8 FRQ practice and Unit 8 practice questions.
Mini FRQ: Biodiversity and Recovery After Disturbance
Prompt
Researchers compare two grassland ecosystems after a drought. Ecosystem A contains 18 plant species with similar abundance. Ecosystem B contains 18 plant species, but one grass species makes up 80% of all individuals. After the drought, Ecosystem A returns to its original biomass within two years, while Ecosystem B remains below its original biomass.
- (a) Identify which ecosystem has higher species diversity. (1 pt)
- (b) Explain why the ecosystems do not have the same species diversity even though they have the same richness. (2 pts)
- (c) Identify which ecosystem shows greater resilience. (1 pt)
- (d) Explain how biodiversity may contribute to recovery after disturbance. (2 pts)
Scoring checklist
- Identifies biodiversity measure.
- Uses evidence from the data.
- Distinguishes richness, diversity, resistance, or resilience correctly.
- Explains a mechanism such as redundancy, alternative food webs, or genetic variation.
- Connects biodiversity to stability or recovery.
- Avoids vague "biodiversity is good" statements.
Point rubric
- (a) Identify which ecosystem has higher species diversity. (1 pt)
- (b) Explain why the ecosystems do not have the same species diversity even though they have the same richness. (2 pts)
- (c) Identify which ecosystem shows greater resilience. (1 pt)
- (d) Explain how biodiversity may contribute to recovery after disturbance. (2 pts)
Model answer
- Ecosystem A has higher species diversity.
- Both ecosystems have the same richness, but Ecosystem A has greater evenness.
- Ecosystem A shows greater resilience because it returns to original biomass faster.
- Biodiversity may provide functional redundancy and alternative species that continue ecosystem function after drought.
Common mistake: Do not say the ecosystems have the same diversity just because they have the same number of species.
Biodiversity and Ecosystem Stability Flashcards
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Biodiversity and Ecosystem Stability Practice Questions
Biodiversity and Ecosystem Stability FAQ
What is biodiversity in AP Biology?
Biodiversity is the variety of life in an area, including species diversity, genetic diversity, and ecosystem diversity. On the AP Biology exam, biodiversity questions often ask you to connect this variety to ecosystem function, disturbance response, or stability.
How does biodiversity affect ecosystem stability?
Biodiversity can increase ecosystem stability because diverse ecosystems often contain more functional roles, genetic variation, and backup pathways. If one species declines, others may partially replace its function or keep food webs operating.
What is species richness?
Species richness is the number of different species in a community. AP Biology data questions may give a species count and ask you to compare richness across communities.
What is species diversity?
Species diversity includes both the number of species and their relative abundance, or evenness. Two communities with the same richness can have very different diversity if one species dominates.
What is the difference between species richness and species diversity?
Species richness counts how many species are present, while species diversity also considers how evenly individuals are distributed among those species. A community with high richness but one dominant species usually has lower diversity.
What is genetic diversity?
Genetic diversity is the amount of genetic variation within a population or species. Higher genetic diversity can help populations survive disease, drought, or other environmental change.
What is ecosystem stability?
Ecosystem stability is the ability of an ecosystem to maintain function during disturbance or recover after disturbance. AP Biology often links stability to resistance, resilience, and biodiversity.
What is resistance in ecology?
Resistance is the ability of an ecosystem to withstand disturbance without major change. A resistant ecosystem may lose little biomass or maintain similar community structure during the disturbance.
What is resilience in ecology?
Resilience is the ability of an ecosystem to recover after disturbance. A resilient ecosystem may drop during the disturbance but return toward its original function or structure afterward.
How do invasive species affect biodiversity?
Invasive species can reduce biodiversity by outcompeting native species, changing food webs, or altering habitat conditions. Adding a nonnative species does not automatically increase meaningful biodiversity or stability.
How do keystone species affect biodiversity?
Keystone species can help maintain biodiversity because they have disproportionately large effects on community structure. Removing a keystone predator, for example, may allow one prey species to dominate and reduce overall diversity.
How should I explain biodiversity and stability on an AP Biology FRQ?
Identify the biodiversity measure in the data and explain whether the ecosystem resists or recovers from disturbance. Then connect the pattern to a mechanism such as functional redundancy, alternative food web pathways, or genetic variation.