Population growth – carrying capacity
Integrated ScienceEcologyAges 13–14
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Ecology
A population (shown as individuals inside an environment box) grows from N₀ at rate r; once limited by carrying capacity K, the curve N(t) becomes S-shaped and levels off around K. Students choose an ecological factor (drought lowers K, abundant food raises K), tap the environment box to trigger a disease outbreak that cuts the population, and watch it recover. The growth formula and data update continuously.
Lesson: Population ecology; Environment and ecological factors
What it shows
Population size changes by births minus deaths, summarised in the growth rate r per generation. With unlimited resources growth is exponential (ΔN/Δt = r·N), so the population doubles again and again. Real environments offer only limited food and space, captured by the carrying capacity K; in the logistic model (ΔN/Δt = r·N·(1 − N/K)) growth slows as N approaches K, giving an S-shaped curve with slow, rapid and stable phases. Ecological factors such as drought or abundant food shift K, and a disease outbreak lowers N, after which the population returns toward the new equilibrium.
How to use
Run the Model Limited by carrying capacity (S-shaped curve) and watch the phase label change as N rises toward K, then switch to Unlimited (exponential growth) and compare the curves. Next, choose drought or abundant food under Ecological factor at generation 12 and note where N settles. Press Disease outbreak (−30 %) once the population is stable and time its recovery. Finally, change Growth rate r while keeping K fixed and see which part of the curve responds.
Parameters you can change
- Initial population size N₀ 2–200 individuals
- Growth rate r (births − deaths) 0.1–2 /generation
- Carrying capacity K 50–1000 individuals
- Model Limited by carrying capacity (S-shaped curve), Unlimited (exponential growth)
- Ecological factor at generation 12 None, Drought: K halves, Abundant food: K increases 1.5×
Questions to explore
- Why can a real population not keep growing exponentially for long?
- After the drought at generation 12, at what size does the population stabilise?
- Does a larger growth rate r change the final stable population size, or only how fast it is reached?
Teaching ideas
All guides- Quadrat Sampling Virtual Lab: Estimate a PopulationA quadrat sampling virtual lab for the GCSE field investigation: estimate a population with random quadrats and map a shade-to-sun change with a transect.
- Mark–Release–Recapture Virtual Lab: The Lincoln IndexA mark–release–recapture virtual lab: estimate a woodlouse population with the Lincoln index, then break one assumption at a time and see the estimate go wrong.
