1Ecosystem words
A habitat is where an organism lives. All the rabbits in a meadow are a population; all the populations there are a community. Add the soil, water and air, and you have an ecosystem.
habitatpopulationcommunityecosystem
Lesson 25.2 notes
Interdependence
Habitats and populations, how a change spreads through a food web, predator and prey cycles, and competition.
2Depending on each other
Organisms depend on each other: for food, for shelter (birds nest in trees), for pollination, and to spread seeds (jays bury acorns). This is called interdependence.
interdependence
3Remove one species
Take the foxes out of the web and more rabbits and mice survive. With more rabbits, more grass is eaten. One change spreads through the whole food web.
4Predators and prey
When there are lots of rabbits, foxes have plenty to eat and more cubs survive. More foxes eat more rabbits, so rabbit numbers fall. Then the foxes go hungry, and the cycle starts again.
5Competing animals
Animals compete for food, water, mates and territory. A robin sings to defend its territory against other robins. The animals best suited to win are the most likely to survive and breed.
competeterritory
6Competing plants
Plants compete for light, water, minerals and space. A tall tree shades the seedlings beneath it, and its roots take up water and minerals from the soil around them.
7Newcomers
Grey squirrels were brought to Britain from North America in the 1800s. They out-compete native red squirrels for food and spread a virus that kills reds, which have vanished from most of England.
Explore: Population lab
Run rabbits and foxes through the years, then let disease strike the rabbits, remove most of the foxes or give the rabbits a good year, and watch both populations respond.
Common mistake: Predators rarely wipe out their prey
As prey get scarce, predators go hungry and fewer survive, so the prey can recover. In a stable ecosystem their numbers often rise and fall in a cycle, the predators peaking just after the prey.
Remember
- A population is all the organisms of one species in an area. All the populations make a community; add the non-living surroundings for an ecosystem.
- Organisms depend on each other for food, shelter, pollination and spreading seeds. A change to one population affects others: this is interdependence.
- Predator and prey numbers often rise and fall in cycles. Animals compete for food, water, mates and territory; plants for light, water, minerals and space.
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