AQA Biology 4.7.1.1 and 4.7.2.1 · Combined and Triple

Population and competition

What plants and animals fight over, what stops a population growing for ever, and a graph where one line always follows the other.

Triple Science · Foundation tier

Start here

One pot, two plants.

Two seedlings are planted together in one small pot. A third seedling gets a pot of the same size to itself.

If you had to guess, which grows bigger: one of the pair, or the one on its own?

Competition

What they fight over.

Plants in a community or habitat often compete with each other for light and space, and for water and mineral ions from the soil. Animals often compete with each other for food, mates and territory. Tap each.

Competition is fiercest between members of the same species, because their needs are exactly the same (competition within a species). It also happens between species: grey squirrels outcompete red squirrels for food and nesting sites (competition between species).

A hedgerow holds hawthorn bushes, blackbirds and robins. Suggest what the blackbirds and robins compete for.

Pick one.

What limits a population

Why numbers stop rising.

A population cannot grow for ever. Its size is limited by the food, water and space available, and by predators and disease. Tap each.

Predator and prey

One line follows the other.

In a stable community the numbers of predators and prey rise and fall in cycles. Pick a year and read the graph. The populations are made up for practice.

Year 0: hares are rising. Plenty of plants to eat, few lynx.

The predator peak comes after the prey peak. Why?

Pick one.

At year 4 the hares are falling fast. What happens to the lynx over the next two years?

Pick one.

Think again · same time?

“Predators and prey go up and down at the same time.”

Your call

Choose

On a predator–prey graph, when does the predator peak come?

Sort

Who competes for what?

Place each resource.

Tap a card, then tap the box it belongs in. Tap a placed card to take it back.

Command words in this lesson

Suggest: What organisms in a given habitat compete for.
Interpret: A predator–prey graph: read values and find the lag.
Explain: Why the predator peak comes after the prey peak.
Describe: What limits a population.

Key fact

Plants compete for light and space, and for water and mineral ions from the soil. Animals compete for food, mates and territory. Predator numbers follow prey numbers, with a lag.

Key note · AQA 4.7.1.1, 4.7.2.1

Population and competition

Plants in a community or habitat often compete with each other for light and space, and for water and mineral ions from the soil.
Animals often compete with each other for food, mates and territory.
You should be able to suggest what the organisms in a given habitat compete for.
A population is limited by food, water, space, predators and disease.
In a stable community the numbers of predators and prey rise and fall in cycles: more prey, then more predators (after a lag, because predators take time to breed), then fewer prey, then fewer predators.

Photograph this card. Tomorrow, cover it and say each line first.

Previous and next

Connects to

Ask MrBadmus

Not sure why the predator line lags?

The hare and lynx numbers are made up for practice.