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5.3Unit 4: Ecosystems

Intruders in an ecosystem — Cambridge Checkpoint Biology 0893 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 4 1 quiz

📚 Cambridge Checkpoint Biology 0893 Hub / Topical Revision
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Lesson summary

5.3 Intruders in an ecosystem — CHECKPOINT BIOLOGY 0893 notes: Explain how an introduced (invasive) species can harm an ecosystem, using New Zealand and the Sonoran Desert as examples.Native species = a species that naturally lives in an ecosystem.Introduced species = a species b…

  • Invasive species
  • To eradicate
  • Introduced species = a species brought by people into an ecosystem where it does not naturally live
  • A new species must fit into the network of interactions in an ecosystem, and this affects the species already there
  • New Zealand separated from all other areas of land about 66 million years ago
  • Because of this separation, its species developed differently from those elsewhere on Earth

Part 1 of 7Native and introduced species

Native species
Native species a species that naturally lives in an ecosystem.
Introduced species
Introduced species a species brought by people into an ecosystem where it does not naturally live.
Invasive species
Invasive species an introduced species that spreads and harms the ecosystem.
A new species must fit into the network of interactions in an ecosystem, and this affects the species already there.

Part 2 of 7Why New Zealand was vulnerable

Why New Zealand was vulnerable
New Zealand separated from all other areas of land about 66 million years ago.
Because of this separation, its species developed differently from those elsewhere on Earth.
Before humans arrived there were no predatory mammals.
  • Many native birds nest on the ground, so their eggs and young were safe.
  • Several native birds, such as the kiwi, cannot fly even as adults.

Part 3 of 7Species brought to New Zealand

1
Humans arrived about 700 years ago and brought animals with them that did not belong there.
2
Rats stowed away on boats and now live in most of the country.
  • They eat birds' eggs and defenceless young birds.
3
Farmers brought sheep for wool and meat.
4
Rabbits were brought on sailing ships as food, but they escaped and ate grass in sheep pastures.
5
Stoats were brought from Europe to control the rabbits.
  • Stoats spread over New Zealand, breed rapidly and are fierce hunters.
  • They can kill birds much larger than themselves.
  • They made several native bird species extinct, including the laughing owl and the New Zealand thrush.
  • They eat almost 60% of kiwi chicks.

Part 4 of 7Effects of invasive species

Effects of invasive species
Scientists think 53 native bird species in New Zealand have become extinct since humans arrived.
  • Hunting by people caused part of this.
  • Introduced invasive species caused most of it.
Native species may decrease or become extinct.
Food webs are disrupted and biodiversity falls.

Part 5 of 7Why introduced species cause problems

1
The native prey may not be adapted to defend against the new predator.
2
The new species may have no natural predators or diseases in the new place.
3
The new species may reproduce quickly and compete strongly with native species for food, space and light.
4
Stoats are not a problem in Europe, where they normally live,
  • because their numbers are limited by other animals and the prey there is adapted to them.

Part 6 of 7Controlling introduced species

To eradicate
To eradicate to get rid of completely.
Eradicating an introduced species is very difficult once it has settled, so the best that can usually be done is to control its numbers.
Methods of control include trapping or culling and removal by hand.
Border checks stop new species arriving.

Part 7 of 7Buffelgrass in the Sonoran Desert

1
Buffelgrass is native to Africa, Asia and the Middle East.
2
It was planted in Arizona in the 1930s as food for cattle.
3
It is now spreading rapidly through the Sonoran Desert, and it is an introduced (invasive) plant.
4
It grows in dense patches and takes water and nutrients from the soil.
  • Native plants have less water and nutrients.
  • Animals that depend on those plants lose food and shelter.

Key terms

TermMeaning
Native speciesA species that naturally lives in an ecosystem.
Introduced speciesA species brought by people to a place where it does not naturally live.
Invasive speciesAn introduced species that spreads and harms the ecosystem.
ExtinctNo longer existing anywhere.
EradicateTo get rid of completely.
PredatorAn animal that hunts and eats other animals.

Avoid these mistakes

1
Saying all introduced species are harmful — only those that spread and harm the ecosystem are invasive.
2
Saying invasive species are always new to science — they are native elsewhere.
3
Believing an introduced species is easy to remove once established — eradication is very difficult.
4
Forgetting that stoats were introduced to control rabbits — a control measure caused a new problem.
5
Thinking humans caused extinctions only by hunting — introduced species caused most of them.

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