Invasive species

An invasive species, also called an invasive exotic, or invasive alien species is an organism that is intentionally or accidentally introduced to an area where it is not native, and where it successfully invades and disturbs natural ecosystems, displacing indigenous and endemic (native) species. The term is applied to both plants and animals.

The best place to study invasives is on isolated islands, such as the Hawaiian Islands. The native ecosystems of islands removed from continental faunas and floras are handicapped to meet the threat of exotic introductions. Often this means that no natural predators are present, and the non-native spreads uncontrollably into an open niche.

Table of contents

1 Invasive Exotic Plants 2 Invasive Exotic Animals 3 Invasive Exotic Diseases 4 Historical Perspective

Invasive Exotic Plants

Many non-native plants have been introduced into the United States and Australia initially as either ornamentals or for erosion control, stock feed, or forestry. Among the more serious invasive exotics are vines, such as kudzu. Whether or not an exotic will become invasive is seldom understood in the beginning, and many non-native ornamentals languish in the trade for years before suddenly naturalizing and becoming invasive.

Some of the most damaging invasive plants in the eastern United States are listed below:

• Lonicera japonica -- Japanese honeysuckle
• Lonicera maackii -- Amur honeysuckle
• Rosa multiflora -- multiflora rose
• Lythrum salicaria -- purple loosestrife
• Pueraria montana -- kudzu (aka Pueraria lobata)
• Celastrus orbiculatus -- oriental bittersweet
• Elaeagnus umbellata -- autumn-olive
• Alliaria petiolata -- garlic-mustard

A major invasive marine species in southern Europe is the seaweed Caulerpa taxifolia. Caulerpa was first observed in the Mediterraneen Sea in 1984, off the coast of Monaco. By 1997, it had covered some 5000 hectares. It has a strong potential to overgrow natural biotopes, and represents a major risk for sublittoral ecosystems. The origin of the alga in the Mediterranean was thought to be either as a migration through the Suez Canal from the Red Sea, or as an accidental introduction from an aquarium.

Invasive Exotic Animals

One of the most egregious examples of introducing an invasive exotic animal was perpetrated by one Eugene Scheiffer, a Shakespeare fan, who deliberately released eighty starlings into Central Park in New York City in 1890, and another forty in 1891. He did so because he wanted to introduce all of the birds mentioned in Shakespeare's plays into the United States! Ironically, the starling had been introduced previously into Ohio and had failed to survive.

A number of invasive exotics in Australia are listed below:

• rabbit
• Brown hare
• European red fox
• common starling
• nutmeg mannikin
• cane toad
• brown trout
• mosquitofish
• honeybee

Other outstanding examples of invasive exotic animals include the gypsy moth in eastern North America, zebra mussel and alewife in the Great Lakes; and the Common Brushtail and Common Ringtail possums in New Zealand.

Invasive Exotic Diseases

History is rife with the spread of invasive exotic diseases, such as the introduction of smallpox into the Americas, where it obliterated entire Native American civilizations before they were ever even seen by the Europeans.

Invasive exotic disease introductions in the past century or so include the chestnut blight which has virtually extinguished the American chestnut, and Dutch elm disease, which has severely damaged the American elm

Historical Perspective

Although it is assumed that invasive species have been a problem since man has been around to carry them, modern invasive species science began with the work of Charles Elton called The Ecology of Invasions, which was published in 1958. The next ground-breaking work dealing with the principles of invasions was Island Biogeography and Conservation Practice by Simberloff and Abele in 1976.

There are several classic accounts of species that have been invaders for many decades. The sea lamprey began to make its way up into the Great Lakes Region when the St. Lawrence Seaway was completed in 1959, devastating the lake trout fishing industry. It continues to be a largely-controlled problem today, but costs millions in lamprecides, traps, physical barriers, and other control methods.

Rabbits were introduced into Australia with colonists in the 1800 and their devastation is ongoing in spite of the famous rabbit fences that were built along thousands of miles of territory with the futile intention of keeping them out.

The often unsuccessful use of biological control provides another historical perspecitive of the invasive species problem. When rats overwhelmed seaports and became crop pests during the 1800's in some islands in the Pacific, mongoose were introduced to control them. The mongoose preferred to eat native species that were easier to catch than the invasive rats, and became invaders themselves. As a result, modern day biological control is used only if extensive studies find that the biocontrol species will not have a negative effect on native populations.

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The term "invasive exotic" is generally not used for economically valuable crops and livestock, although they can have larger effects on ecosystems than even the most successful of unintentionally introduces species.

See also

• Rabbit invasion in Australia
• Biodiversity