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There's an Alien in My Pond!

Biologists don’t believe in aliens from outer space but there are aliens they do know about. They are the alien or invasive species that are spreading around the world seeking new homes in faraway places that cannot always cope with them.

Invasive species are defined as non-native species that have been introduced to a habitat, usually as a result of human activity, and have become established. Often they pose a real threat to the long-term survival of native species because they have no natural enemies and can out-compete local species.

You might be surprised to learn that one invasive species is the common brown rat. Not a problem in most places, but on the Antarctic island of South Georgia where they were accidently introduced by travellers in the 18th century they have become a menace. Rats have no natural enemies on the island, which is home to several indigenous species not found anywhere else. One that has suffered badly is the rare pintail duck whose eggs and chicks are a favourite food of the rats. A long running project, due to complete next year, is underway to eradicate the rats and save the ducks.

Albatross are another species threatened by unwanted aliens in their Saint Helena home. This time the alien is tiny, the house mouse which will eat albatross and petrel chicks.This sounds like fiction because the chicks are ten times the size of a mouse, but several mice nibbling at one helpless youngster can soon kill it. These deaths have a devastating effect on the birds’ population because albatross only produce one chick every two years.

Many other aliens are carried about the world along international trade routes. Ballast tasks take in marine organisms from all over the world and others hitch hike on hulls or in fishing equipment. One of the best known is the freshwater Zebra mussel that travelled by ship from the Black Sea to the Great Lakes of the USA. Since the 1980s they have multiplied and trillions of them clog water pipes and block power station inlets. Once they even cut off the water supply to a whole town.

This month a new alien, a relative of the Zebra mussel, has been found in the U.K. The quagga mussel (Dreissena rostriformis) also blocks pipes, causing flooding and affecting water quality. Quagga cluster together in huge colonies that can be almost impossible to remove. And a Quagga mussel can live for up to five years and produce over five million eggs.

Mussels pose one threat but three alien shrimp with chilling names: the killer, the demon and the bloody red shrimp have come along too. Killer shrimp feed on the waste from mussels and their bodies are shaped and camouflaged to hide amongst them. The new invaders gain a mutual benefit from their inter-specific interactions and their presence has consequences on many other animals further along the food chain. 

If you study option C in your IB course you will learn more about invasive species such as cane toads and prickly pear in Australia and plants such as rhododendron and Japanese Knotweed in Europe. You can find out more about some of the measures that are used to try and control them.

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Author Spotlight

Brenda Walpole

Brenda Walpole has 20 years experience of teaching IB biology and has written over 30 science books. She is currently an independent consultant in science education.

Brenda Walpole has 20 years' experience of teaching IB Biology and has written over 30 science books. She is currently an independent consultant in science education. - See more at: /uk/subject/science/biology/biology-for-the-ib-diploma-(second-edition)#sthash.NYgv0XOF.dpuf
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Related Resource

Biology for the IB Diploma (second edition)

Brenda Walpole, Ashby Merson-Davies and Leighton Dann

Covers in full the requirements of the IB syllabus for Biology for first examination in 2016.

Published/Available: March 2014


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