Unit 3: Populations
AP Environmental Science: 52 practice questions with detailed explanations.
Unit Study Guide
Executive Summary
Unit 3 applies population ecology to humans and other species: growth models, life-history strategies, and demographic transition.
Species strategies
Generalists (raccoons, humans) tolerate wide conditions and varied diets; specialists (pandas, koalas) need narrow niches and are more extinction-prone. r-selected species produce many offspring with little care; K-selected species produce few with heavy investment.
Survivorship and growth
Survivorship curves: Type I (most survive to old age — humans), Type II (constant mortality — birds), Type III (most die young — oysters). Populations grow exponentially when unlimited, logistically as they approach carrying capacity (K), which is set by limiting resources. Density-dependent factors (disease, competition) bite harder in dense populations.
Human demographics
Age structure diagrams (pyramids) reveal growth momentum: wide bases grow, narrow bases decline. The demographic transition moves from high birth/high death rates, through falling death rates (population boom), to low birth/low death rates. Total fertility rate (TFR) and replacement-level fertility (~2.1) predict future size; the IPAT equation links impact to population, affluence, and technology.
Exam traps
r/K strategies are ends of a spectrum, not rigid boxes. Carrying capacity can change with technology or resource depletion. A shrinking population can still grow for decades if its age structure is bottom-heavy (population momentum).