Ecosystem Interactions
- Biology
- Ages 11–14 · Grades 6–8
What you’ll find out
- Competition for limited resources controls population sizes.
- Predator and prey populations rise and fall in linked cycles.
- Symbiosis includes mutualism, parasitism and commensalism.
No sign-up and no real names. In the lesson you check your understanding as you read, and practise until it sticks.
Competition and predation
Living things in an ecosystem constantly affect one another. When organisms need the same limited resource, such as food, water, light or space, they compete, and the resource limits how many can survive. Predation is when one animal, the predator, hunts and eats another, the prey. Predator and prey numbers are linked. In northern Canada, when snowshoe hares are plentiful, lynx thrive and multiply. As more hares are eaten, their numbers crash, so lynx starve and decline, which then allows hares to recover.
Living together: symbiosis
Some species live in very close relationships, which scientists call symbiosis. In mutualism, both partners benefit: a clownfish shelters among a sea anemone’s stinging tentacles, safe from predators, while it chases off fish that would eat the anemone. In parasitism, one partner, the parasite, benefits while harming its host; ticks and tapeworms are parasites. In commensalism, one partner benefits while the other is neither helped nor harmed, as when barnacles ride on a whale to reach new feeding grounds.
Curriculum links: NGSS MS-LS2-1 · NGSS MS-LS2-2 · England KS3: Interactions and interdependencies · Cambridge Lower Secondary Stages 7–9: Biology · NCERT Science, Classes 6–8