Concept check: What is an invasive alien species?

Throughout history people have been on the move, colonizing different parts of the world. Wherever we go, we take with us the plants and animals that we depend on for food, transport, medicine, building, crafts and pleasure. Sometimes weeds and pests that we donít want hitch a ride with us. Whether on purpose or by accident, we have introduced many alien species to places on Earth where they did not occur naturally.

Sometimes these introductions have failed - the conditions in the new country have not suited the introduced species and it has been unable to survive. Other introduced species have needed our help to survive (e.g. some garden plants, agricultural crops and domestic animals). But some plants, animals and micro-organisms have found conditions in their new homes to be so favourable that they have become invasive. Today, the spread of invasive alien species is one of the greatest threats to people and nature worldwide.







Why are invasive alien species a problem?
Invasive alien species grow and reproduce very successfully in their new habitat, but lack the natural predators, parasites and diseases that would normally control their numbers in their home countries. This gives them an unfair advantage over indigenous species.







How do invasive alien plants harm biodiversity ?
Look at the pictures below and try to explain how an alien plant invading a natural area can threaten natural biodiversity.






In this section we will find out about some of the invasive alien plants and animals that are threatening people and nature in the lowlands of Cape Town. For more information on invasive alien species, go to
Click the buttons to find out more about invasive alien species in Cape Town:
Terrestrial plants:      Aquatic plants Terrestrial animals: Aquatic animals
Kikuyu Grass Water Hyacinth Argentine Ant Largemouth Black Bass
Port Jackson Willow Parrot's Feather European Starling Common Carp
Rooikrans Spanish Reed Feral Cat European Mallard