Unit 2: The Living World: Biodiversity
AP Environmental Science: 52 practice questions with detailed explanations.
Unit Study Guide
Executive Summary
Unit 2 covers the variety of life, the services it provides, and how disturbance shapes ecosystems through succession.
Biodiversity levels
Genetic diversity (variation within a species), species diversity (richness + evenness), and ecosystem diversity (habitat variety). Higher diversity generally means greater resilience to disturbance.
Ecosystem services
Provisioning (food, timber, medicine), regulating (climate, flood control, water purification), supporting (nutrient cycling, soil formation), and cultural (recreation, aesthetics). Biodiversity underwrites all four.
Island biogeography
Species richness on islands balances immigration (higher near the mainland) against extinction (higher on small islands). Big, close islands hold the most species; this theory guides reserve design.
Ecological tolerance and disturbance
Each species tolerates a range of conditions (temperature, salinity, pH) — its fundamental niche. Natural disturbances (fire, floods, storms) reset communities; many ecosystems depend on periodic disturbance.
Succession
Primary succession starts on bare rock with no soil (lichens → mosses → soil). Secondary succession follows disturbance where soil persists. Pioneer species give way to a climax community over time. Intermediate disturbance often maximizes diversity.
Exam traps
Species richness alone misses evenness — a community dominated by one species can be low in diversity despite many species present. Tolerance curves show ranges, not single values. Disturbance is not always bad; fire-adapted ecosystems need it.