Transportation of plants and animals from one ecosystem to another where the native plants and animals have no evolutionary experience with them has had catastrophic effects. For example, goats were introduced to the island of St. Helena in the South Atlantic, where heavy forests once covered the land. However, after timbering, the goats ate the seedlings, prevented regrowth, and converted the island to a rocky wasteland by early in the last century. On Santa Catalina Island off the coast of California, goats helped destroy forty-eight indigenous and eighteen exotic species of plants. And with the disappearance of the plants went the associated animals.
The native plants and animals of New Zealand and Australia have been ravaged by imported floras and faunas. The Eastern Bluebird of North America (on the left) has gone into serious decline because of overwhelming competition for nesting holes from two introduced birds - the Starling and the House Sparrow. Cabbage Butterflies from Europe may have outcompeted the populations of native Cabbage Butterflies in North America. The importation of the American Gray Squirrel has annihilated the native red one from large areas of England. Dutch elm disease, brought from continental Europe, has killed many populations of English and American elms. The Chestnut Blight, a type of fungus, accidentally brought to the United States, had pushed American Chestnut trees virtually to extinction. The zebra mussel, first discovered in North America in Lake Saint Clair, Ontario, Canada, in 1988, is rapidly spreading to most of the major freshwater ecosystems of the eastern United States, altering aquatic ecosystems and displacing native mollusks at an alarming rate along the way. In 1959 British colonists introduced the Nile perch into Lake Victoria in eastern Africa as a sport fish, but this large predator has drastically reduced native fish populations and caused the extinction of as many as 200 endemic species of cichlid fish. Because the cichlids are important algae-feeding fish, the lake has since become choked with decomposing aquatic vegetation, depleting the oxygen in the water and leading to further species declines and harm.
Indirect Causes - Development
