Population growth curves explains how ecological evidence links organisms, resources and interactions to population size, distribution or community structure in a habitat.
Coverage 2012–2023 · Updated 16 Jul 2026
Population growth is exponential while resources are abundant and limiting factors are weak, but becomes sigmoid as density-dependent limits slow growth near carrying capacity.
During exponential growth, a roughly constant per-capita growth rate produces an increasingly steep rise. In a sigmoid model, competition and other density-dependent factors reduce net growth until births plus immigration balance deaths plus emigration near carrying capacity.
Test exponential growth by plotting population size on a logarithmic vertical axis against time on a linear horizontal axis: exponential data form an approximately straight line. For the IB sigmoid model, a separate lag phase is not expected.
An introduced population with abundant food may initially show a straight line on the semi-log graph; later points fall below that line as resource limitation increases and the population approaches a plateau.
A population curve is an idealized model, not a guaranteed trajectory. A steep slope means rapid change, not the greatest population size; migration, seasons and disturbances can alter the pattern.
This objective is assessed through essay response, commonly using Draw / Identify / Label.
Draw / Identify / Label / Outline / State / Explain / Discuss / Suggest / Compare
Build the answer around this relationship: Population growth curves must be linked to the correct ecological unit, method or species interaction.
Confusing a population with a community or with all organisms in an ecosystem.
Representative question
Discuss the factors affecting population growth that can result in an exponential growth curve.
