WACE Biology — Year 11 Unit 1
Population Dynamics — Flashcards & Quiz
Population dynamics studies how populations change over time in response to births, deaths, immigration and emigration. WACE Biology Year 11 Unit 1 asks you to distinguish exponential from logistic growth, apply the concept of carrying capacity, and explain density-dependent and density-independent factors that regulate populations. Predator-prey cycles are a standard exam context.
Key Points
- Population change: ΔN = (Births + Immigration) – (Deaths + Emigration).
- Exponential growth: J-shaped curve; occurs when resources are unlimited. dN/dt = rN.
- Logistic growth: S-shaped curve; growth slows as population approaches the carrying capacity K. dN/dt = rN(K–N)/K.
- Carrying capacity (K): maximum sustainable population size for an environment given available resources.
- Density-dependent factors: effects increase with population density — competition, disease, predation.
- Density-independent factors: effects are independent of density — weather events, natural disasters, habitat destruction.
Common Mistakes to Avoid
- Confusing exponential (unlimited resources) with logistic (carrying capacity) growth.
- Using "population density" interchangeably with "population size" — density is per unit area.
- Classifying disease as density-independent — it's usually density-dependent because transmission rises with density.
- Forgetting carrying capacity is not fixed — it varies with environmental conditions.
- Drawing predator-prey cycles without the predator lag behind the prey peak.
Exam Strategy
SCSA Unit 4 population dynamics questions often give you a graph of population over time and ask you to interpret it. Method: (1) identify the growth phase (exponential, logistic, stable, decline), (2) name the factors affecting it, (3) distinguish density-dependent from density-independent drivers. For predator-prey questions, always note the lag and the cyclical pattern.
Sample Flashcards
Q1: Distinguish between exponential growth and logistic growth in populations.
Exponential growth (J-curve) occurs when resources are unlimited — the population grows without constraint at a constant rate (dN/dt = rN). Logistic growth (S-curve) occurs when resources are limited — growth slows as the population approaches the carrying capacity (K), where birth rate equals death rate: dN/dt = rN((K−N)/K).
Q2: What is carrying capacity and what factors determine it?
Carrying capacity (K) is the maximum population size that an environment can sustain indefinitely given available resources. It is determined by limiting factors: density-dependent factors (competition, predation, disease, parasitism — intensify as population grows) and density-independent factors (natural disasters, climate events, fire — affect populations regardless of size).
Q3: Explain the difference between r-selected and K-selected species.
r-selected species: high reproductive rate, many small offspring, little parental care, short lifespan, rapid maturity, thrive in unstable environments (e.g. insects, weeds, bacteria). K-selected species: low reproductive rate, few large offspring, significant parental care, long lifespan, late maturity, thrive in stable environments near carrying capacity (e.g. elephants, whales, humans).
Sample Quiz Questions
Q1: Exponential population growth can continue indefinitely in any environment.
Answer: FALSE
Exponential growth cannot continue indefinitely because resources are finite. Eventually, limiting factors (food, space, water, disease, predation) slow growth, and the population approaches its carrying capacity — resulting in logistic growth.
Q2: Carrying capacity is the maximum population size an environment can sustain indefinitely.
Answer: TRUE
Carrying capacity (K) represents the maximum number of individuals an environment can support long-term, given its available resources. The population fluctuates around K as conditions change.
Q3: Disease and competition are examples of density-independent limiting factors.
Answer: FALSE
Disease and competition are density-DEPENDENT limiting factors — their effects intensify as population density increases. Density-independent factors (e.g. bushfire, drought, flood) affect populations regardless of their size.
Revision Tip
Population growth curves are visual — drill a Revizi deck of graph-interpretation questions covering exponential, logistic and predator-prey patterns.
Last updated: March 2026 · 3 flashcards · 3 quiz questions