Alien species threaten biological diversity

Posted: 21 May 2001

"Invasive alien species are thought to be the biggest threat to biological diversity after habitat destruction," said Klaus Toepfer, Executive Director of the United Nations Environment Programme.

The dramatic growth in tourism and trade is offering these unwanted visitors more and more opportunities to travel hundreds or thousands of kilometres beyond their natural habitat via boat or aircraft. Some thrive in their new homes - but at great cost to native species and ecosystems, and at a cost of billions of dollars to local economies," he said.

Strawberry guavaThe strawberry guava is native to Brazil but has been naturalised in Florida, Hawaii, tropical Polynesia, Norfolk Island, and Mauritius for its edible fruit. It has had a devastating effect on native habitats on Mauritius and is considered the worst pestplant in Hawaii.© Wendy Strahm/IUCNInvaders can compete with native plants and animals, displace them, consume them, act as parasites or transmit diseases, reduce growth and survival rates, cause the decline or extinction of local populations or even entire species, and uproot or damage plants.

"While alien species are an age-old problem, we are only now starting to fully appreciate the havoc they cause," said Hamdallah Zedan, Executive Secretary of the Convention on Biological Diversity, which was adopted in 1992 under UNEP auspices.

"If we are to succeed in stemming the tide of invasives, we will need more scientific work and more awareness-raising. Only when people fully realize what is happening and what is at stake can we begin to reverse the destruction."

Under the Convention, governments are working together to take more aggressive measures to prevent alien species from invading in the first place. If this fails, complete removal may still be feasible very early in an invasion. Where eradication is not feasible or cost-effective, containment and long-term control measures will need to be considered.

But governments cannot do it alone. Businesses and individuals have a vital role to play. Tourists must take the responsibility for obeying all customs rules - even a piece of fruit in hand luggage can carry invading insects or micro-organisms - and owners of exotic pets or plants must take care to keep them contained. Businesses involved in timber, agriculture, shipping, and similar trades need to rigorously respect safety measures for minimizing the transport of invasive alien species.

There are thousands of examples of invasive alien species. Here are just a few:

  • Introduced fish can eliminate native species and reduce biodiversity. It has been estimated that 20per cent of all freshwater fish species are at risk of becoming extinct in the near future unless the present situation is reversed.

  • Invasive plant species cover an estimated 100 million acres in the US and are spreading annually across three million additional acres, an area twice the size of Delaware. US farmers spend billions of dollars every year on pesticides to destroy invasive plants and weeds.

  • The Hibiscus mealybug, Maconellicoccus hirsutus, has invaded the Caribbean and is attacking a range of plants, including fruit and forestry trees.

  • The corn rootworm, Diabrotica virgifera, was accidentally introduced into the Balkans in the late 1990s during the conflict there; this pest is now spreading and threatening the region's maize production.

  • The invasive sea lamprey has caused trout and other fish stocks in the Great Lakes to collapse. Canada and the US spend $13 million a year attempting to control this pest.

  • $4.5 million is devoted annually to implement a comprehensive inter-agency program to prevent the spread of the brown tree snake and control this pest on Guam.

  • The Weed Science Society of America recognizes about 1,200 plant species as weeds in Canada and the US. Of these, about 65per cent in the US are non-natives.

  • In the Galapagos Islands - a World Heritage Site that is renowned as a natural showcase of evolution - the number of introduced plants is almost as high as the number of natives due to introduced mammalian predators and herbivores as well as insects and plants.

  • In the Eurasian part of the Arctic, the alien Racoon dog, Nyctereutes procyonoides, is multiplying and consuming large numbers of various small mammals. It is also spreading rabies.

  • Prosopis (Mesquite) in the Thar desert of India has displaced other flora of the area, while the specie introduced to a semi-arid area Sri Lanka in the early 1950s, has become an invasive seriously threatening the biodiversity of the only Ramsar-listed wetland of the country.

Extensive information on alien invasive species is available from the:

  • Convention on Biological Diversity
  • Global Invasive Species Programme and
  • World Conservation Union