Introduced species has contributed to close to 40% of extinctions since 1750, ranking second only to habitat loss as a cause for loss of biodiversity.
Intentional and Accidental Species Introduction
Some species were introduced intentionally while other animals stowed away on ships and were accidentally introduced to new lands. European red foxes were introduced intentionally to Australia in the 1800s for the sport of fox hunting. Unfortunately, the red fox preyed on native wildlife contributing to extinctions.
The brown tree snake was introduced accidentally to Guam. This reptile ‘stowed away’ on cargo ships after World War II and preyed on several species of bird and lizard contributing to the extinction of 12 bird species and 6 lizard species from the area.
The Japanese plant kudzu was introduced by the U.S Department of Agriculture to the American South in the 1930s. The purpose was to control erosion but instead the invasive kudzu plant took over large areas of the southern landscape.
Introduced Mammal Species
While there have been numerous plants, animals and insect species introduced to new lands, let's take a look at a few mammals species that have been introduced. Some mammals that have been introduced to foreign lands include:
- Dingo (possibly)
- Cow
- Sheep
- Goat
- Foxes
- Horse
- Rabbit
- Rats & Mice
The Australian dingo is regarded as a species in its own right, and though its origin is not certain, scientists believe it to be related to Middle Eastern and Asian wolves brought to Australia 3500-4000 years ago by Asian seafarers and domesticated by the Aboriginals, though the dingo has since reverted back to a wild dog.
European cows are believed to be descended from a now extinct species of oxen and sheep are descended from mouflon. From their beginnings in the Middle East, new breeds of cows and sheep have been introduced to all corners of the world.
Cows, sheep and other farm animals were introduced to Europe and have been bred to develop desirable characteristics such as good milk production, lean meat, desirable temperament and thick fleece.
Another example is the goat, which was domesticated from the Asian Ibex and introduced to North Africa around 3000 years ago. These goats adapted well to their new environment, feeding on dry scrublands and turning even more of North Africa to desert.
European settlers introduced horses to the Americas and both the settlers and native people used horses to hunt bison. The ancestors of domestic horses are now extinct but groups of horses escaped captivity and now roam free, commonly known as mustangs.
While many mammals were introduced to new lands on purpose as pets or livestock, others, like the rat and mouse stowed away on ships. Rats and mice have been hugely successful in adapting to almost any destination they have been introduced to. The house mouse is in fact the second most widespread mammal in the world, second only to humans.
The black rat spread throughout the world originating from Asia. Fleas that these rats carried also carried and spread the disease the bubonic plague (Black Death) that killed millions of people. The brown rat is thought to have spread from Europe but now exists all over the world. The rodent’s success is due to the fact that it eats almost anything and reproduces at a prolific rate.
So while many deliberate introductions of species were to the benefit of humans, some didn’t quite work that way and the native species must adapt or face extinction.
Resource and further reading:
You may also be interested in The WWF’s Top Ten List of Threatened Species for 2010.
Campbell and Reece, 2002, 'Conservation Biology', in Biology 6th edition, ed. Benjamin Cummings, San Francisco, chap 55.
Roberta Goli - Roberta has a Bachelor of Science Degree (Zoology), has worked with animals for over 10 years and enjoys writing short stories and flash ...
