When growth meets limits.

A population can grow quickly when resources are abundant. As density rises, competition, disease and limited food or space may reduce growth. A logistic model approaches a carrying capacity, but real populations fluctuate.

Births and immigration add individuals; deaths and emigration remove them. Changes in these rates alter abundance. A carrying capacity is context-dependent, not a permanent fixed number.

INTERACTIVE MODEL

Population growth

Model carrying capacity 100; growth slows as N approaches KCarrying capacity10050200

Explore: Change carrying capacity and compare the growth trajectory.

\Delta N=B+I-D-E

WORKED EXAMPLE

A population has 30 births, 10 immigrants, 15 deaths and 5 emigrants.

Add gains: 30 + 10 = 40.
Subtract losses: 15 + 5 = 20, so net change is +20.

Assumed knowledge

Population counts and graphs.

Learning checkpoints & source

YOUR LEARNING CHECKPOINT

Compare exponential and logistic growth.
Identify limiting factors and carrying capacity.

QCAA Biology · Unit 3 · Biodiversity and populations ↗

READY TO TRY IT?

When growth meets limits.

Population growth

A population has 30 births, 10 immigrants, 15 deaths and 5 emigrants.

Put the idea to work.