Unit 2 Biodiversity Tap / Space to flip
Unit 2 Variety of life at three levels: genetic (within species), species (within community), and ecosystem (across landscape).
Unit 2 · 6–8% of exam
The Living World: Biodiversity
Three levels of biodiversity, ecosystem services, island biogeography, ecological succession, resilience, and species roles.
Must-know content
- Three levels of biodiversity: genetic (within species), species (within community), ecosystem (across landscape). Higher diversity → greater resilience.
- Ecosystem services:
- Provisioning — food, water, lumber, fuel.
- Regulating — climate, flood, disease, pollination.
- Cultural — recreation, aesthetic, spiritual.
- Supporting — nutrient cycling, soil formation, primary production.
- Island biogeography — larger islands support more species (more habitat); islands closer to the mainland have higher immigration rates and lower extinction.
- Ecological tolerance — range of conditions (T, pH, salinity, water availability) within which an organism can survive.
- Adaptations and natural selection drive long-term species change.
- Ecological succession:
- Primary — bare rock with NO soil (after volcanic eruption, glacial retreat). Pioneer species: lichens, mosses.
- Secondary — disturbance leaves soil intact (forest fire, abandoned farmland). Faster recovery.
- Climax community — stable end-stage.
- Keystone species — disproportionate community impact (sea otters, wolves, elephants).
- Indicator species — sensitive to environmental change; signal ecosystem health (amphibians, lichens, mayflies).
Example questions
MCQ Which is an example of a provisioning ecosystem service? (A) Pollination (B) Timber from forests (C) Climate regulation (D) Recreation
Answer: B. Provisioning services are tangible products (food, water, lumber, fuel). Pollination and climate regulation are regulating; recreation is cultural.
FRQ Describe the difference between primary and secondary succession and give an example of each.
Answer: Primary succession begins where no soil exists (e.g., after a glacier retreats or volcanic lava cools). Pioneer species like lichens and mosses break down rock to form soil over centuries. Secondary succession occurs after a disturbance where soil remains (e.g., after a forest fire or on abandoned farmland). Regrowth is much faster because soil and a seed bank are already present, so pioneer grasses and shrubs can establish in just years.
MCQ Removal of sea otters from a kelp forest leads to: (A) Increase in kelp growth (B) Sea-urchin population explosion and kelp decline (C) No measurable change (D) Increase in fish biomass
Answer: B. Sea otters are a classic keystone species. Without them, sea-urchin populations explode and overgraze kelp, collapsing the kelp forest and the species that depend on it.
Drill flashcards
Unit 2 Ecosystem services Tap / Space to flip
Unit 2 Free benefits ecosystems provide: provisioning (food, water), regulating (climate, flood), cultural (recreation), supporting (nutrient cycling).
Unit 2 Island biogeography Tap / Space to flip
Unit 2 Larger islands and those closer to mainland support more species (immigration up, extinction down).
Unit 2 Primary succession Tap / Space to flip
Unit 2 Community development on bare rock with no soil (e.g., after volcanic eruption or glacial retreat). Pioneer species: lichens.
Unit 2 Secondary succession Tap / Space to flip
Unit 2 Community recovery after disturbance where soil remains intact (e.g., after a forest fire or abandoned farmland).
Unit 2 Keystone species Tap / Space to flip
Unit 2 Species whose impact on community structure is disproportionately large relative to its biomass (e.g., sea otters in kelp forests).
Unit 2 Indicator species Tap / Space to flip
Unit 2 Species sensitive to environmental change; their presence/absence signals ecosystem health (e.g., amphibians, lichens).
Unit 2 Edge effects Tap / Space to flip
Unit 2 Different conditions at habitat boundaries (more wind, light, predators) — fragmentation increases edge and reduces interior habitat.