Predator and prey cycles

• A predator is an animal that hunts, kills, and eats other animals.

• The animal that is eaten is called the prey.

Example:

• A fox (predator) hunts and eats rabbits (prey).

Predator and prey numbers are both biotic factors.

Here’s why:

• Biotic factors are the living parts of an ecosystem that can affect other organisms.

• Predators and prey are living organisms, so they are biotic factors.

• For example:

• Predators can affect prey population sizes (e.g., more foxes → fewer rabbits).

• Prey numbers can affect predator population sizes (e.g., lots of rabbits → more food for foxes).

Key Adaptations of Predators

Predators have adaptations to help them hunt, catch, and kill their prey, such as:

• Sharp teeth and claws - to catch, hold, and kill prey (e.g. lions, foxes).
• Forward-facing eyes - for good depth perception and judging distance.
• Fast and agile bodies - to chase and catch prey.
• Camouflage - to sneak up on prey without being seen (e.g. tigers in long grass).
• Good senses - excellent hearing, smell, or night vision to locate prey.
• Venom or powerful jaws - in some species, to subdue prey quickly (e.g. snakes).

Key Adaptations of Prey

Prey animals have adaptations to help them detect predators and escape, such as:

• Eyes on the side of their head - gives a wide field of view to spot predators early.
• Camouflage colouring - to blend in and avoid being seen (e.g. white snowshoe hares in the snow and ice).
• Fast and agile - able to run, hop, or fly away quickly.
• Live in groups / herds - ‘safety in numbers’ helps spot predators sooner.
• Warning signals - some prey have bright colours to warn they’re poisonous (e.g. ladybirds).
• Mimicry - some prey mimic more dangerous animals (e.g. harmless hoverflies that look like wasps, so predators believe they may sting them!).

• In a stable community, the numbers of predators and prey go up and down in linked cycles.

• The cycle happens because the populations depend on each other.

How it works:

1. Plenty of prey → predator numbers increase
   There is lots of food, so more predators survive and reproduce.

2. More predators → prey numbers fall
   More predators means more prey are eaten.

3. Fewer prey → predator numbers fall
   Less food means some predators starve or don’t reproduce.

4. Fewer predators → prey numbers rise again
   With fewer predators hunting them, the prey population recovers.

5. The cycle repeats.

How to Interpret a Predator–Prey Graph

When you see a predator–prey graph:

• The prey population always peaks before the predator population.

• This is because predators take time to grow, reproduce and raise young, the predator population increases after the prey population peaks.

Practice Question