What Is an Introduced Species? - Definition, Effects & Examples

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  • 0:02 Introduced Species
  • 1:39 Effects
  • 1:56 Positive Impacts
  • 2:51 Negative Impacts
  • 4:00 Lesson Summary
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Lesson Transcript
Instructor: Marta Toran

Marta has taught high school and middle school Science and has a Master's degree in Science Education.

African killer bees almost wiped out the European honeybee population in the U.S. Whether accidentally (killer bees) or deliberately (European bees), introducing species to a new area can have drastic consequences. This lesson explains why.

A Look at Introduced Species

Introduced species, also called alien species, are those that have been moved by humans to an environment where they didn't occur naturally. The term can refer to animals, plants, fungi, or microorganisms that are non-native to an area. Species introduction can be accidental or intentional.

Many accidental introductions of species involve boats, which travel between continents. For example, the black rat, which is native to South Asia, has been hitching rides in ship cellars since the first century, spreading initially to Europe and subsequently throughout the rest of the world during the Age of Discovery. Species have also been accidentally introduced through water discharged by cruise ships and tankers, stuck to travelers' clothes and shoes, or in imported wood and food.

Sometimes species that don't occur naturally in a habitat are deliberately introduced by humans for conservation efforts, population control of native species, or for boosting agriculture and fisheries. For example, although the U.S. is today the largest producer of corn in the world, and corn is grown in every continent, corn didn't used to exist anywhere but the Mexican mountains until Indians and explorers started taking it to other places. Sometimes species are introduced seemingly on a whim for human enjoyment, like the water hyacinth, which is originally from South America and has been used to beautify ponds in North America, Africa, Asia, Australia, and New Zealand.

Effects of Species Introduction

Species introduction can have drastic social, economic, and environmental effects. Some of these are positive but more often they are negative, such as the disruption of the natural balance of ecosystems. However, let's take a look at some of the positive and negative impacts.

Positive Impacts

One positive impact is increased food production. Americans would have a much more limited menu if it weren't for the introduction of livestock, such as cows, chickens, and pigs, and food products, such as tomatoes, potatoes, pears, and wheat from other parts of the world. Honeybees, too, were introduced from Europe and Africa.

Other than increased food production for the area, species introduction can yield economic benefits from exports and employment opportunities. Chile, for example, is the second greatest producer of salmon in the world and salmon fisheries there employ tens of thousands. However, salmon didn't exist there naturally; it was introduced from Europe, Norway, and Japan. Introduced trees may provide a habitat for many native species of birds, small mammals and invertebrates, and shelter for larger animals.

Negative Impacts

Among the negative impacts of species introduction are mixing of genes, which leads to diluting of native characteristics and habitat modification. The European rabbit was brought to Australia by a nostalgic Englishman who wanted to be reminded of home and make bunny stew occasionally. It led to huge environmental problems when the rabbit population got out of control due to overgrazing and consequent soil erosion.

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