Intruders in an Ecosystem
🎯 In this topic you will
- Learn about how new or invasive species can affect an ecosystem
🧠 Key Words
- eradicate
- extinct
- invasive species
- native species
Show Definitions
- eradicate: To completely remove or destroy something, especially a harmful species from an area.
- extinct: A species is extinct when there are no living members left anywhere in the world.
- invasive species: A species that is introduced to a new environment where it spreads quickly and harms native species or ecosystems.
- native species: A species that naturally lives and evolves in a specific area or ecosystem.
🌍 New Species in an Ecosystem
In your studies of ecosystems, you have seen how all the different organisms interact with each other and their environment. In this topic, you will find out what happens if a new species suddenly arrives. How does the new species fit into the network of interactions? How does this affect the species already there?
🧪 Did you know?
Invasive species are one of the leading causes of biodiversity loss worldwide — even more impactful than habitat destruction in some regions.
🌏 Introduced Species in New Zealand
New Zealand is a country in the Pacific Ocean. New Zealand became separated from all the other areas of land in the world about 66 million years ago. Because of this separation, the species that developed in New Zealand were different from those elsewhere on Earth.
🕊️ Birds Without Predators
Before humans arrived in New Zealand, there were no predatory mammals there. Many of the native species of birds nest on the ground. There were no predators to eat their eggs, so the eggs and young birds were safe. Even the adults of several species of native bird — such as the kiwi — cannot fly.
⛵ Arrival of Humans and New Animals
Nobody knows exactly when humans first arrived in New Zealand, but it was probably about 700 years ago. Humans brought species of animals with them that did not belong in New Zealand. For example, rats stowed away on their boats. Rats now live in most of the country. The rats eat birds’ eggs and defenceless young birds.
📌 Important Concept
Species Vulnerability in Isolated Ecosystems: In ecosystems with no natural predators, species may lose defensive traits like flight or camouflage. The sudden arrival of predators—often through human activity—can cause rapid population decline or extinction.
🐇 Problem with Rabbits and Stoats
Since then, other species have been introduced to New Zealand. Farmers brought sheep, to farm for their wool and meat. Rabbits were brought on sailing ships, to use as food. But the rabbits escaped and began to eat grass in the sheep pastures. So people brought stoats from Europe to control the rabbits.
🦉 Stoats as Invasive Predators
Now stoats have spread all over New Zealand. They are fierce hunters and breed rapidly. They can kill and eat birds much larger than themselves. Stoats have made several species of native bird extinct, including the laughing owl and the New Zealand thrush. Stoats eat almost 60% of kiwi chicks.
🚫 Trying to Control the Damage
People in New Zealand are now trying to eradicate (completely get rid of) stoats, but this is very difficult to do. The best that can be done is to control their numbers.
🧬 Impact on Native Bird Species
Scientists think that 53 species of native bird in New Zealand have become extinct since humans arrived. The extinctions have been partly caused by people hunting and killing the birds, but mostly because of introduced invasive species.
⚠️ Common Mistake
Be careful not to assume that extinction is only caused by hunting — introduced species like stoats often have a much bigger impact.
❓ QUESTIONS
1. In your own words, explain what a ‘native species’ is.
👀 Show answer
2. Name some native species in your own country.
👀 Show answer
3. Suggest why it is very difficult to eradicate an introduced species, once it has settled into a new place.
👀 Show answer
4. Buffelgrass is native to Africa, Asia and the Middle East. It was planted in Arizona in the 1930s, as food for cattle. Now, it is spreading rapidly through the Sonoran Desert.
What is the name for a plant, such as buffelgrass, that is growing in an ecosystem where it does not belong?
👀 Show answer
5. Buffelgrass grows in dense patches. It takes water and nutrients from the soil.
Look at the picture that you made in Topic 4.1, showing interactions in the Sonoran Desert. Suggest how buffelgrass could affect some of the native species in the desert.