When a species ends up in a new environment, it may or may not survive. If it does survive, it may do too well.
In most cases, a species fails to survive in a new environment. Usually conditions do not favor its survival. But in a few cases, a species manages to thrive. It may not have natural predators in the new environment. Or it may kill native species that have no defenses against it. Or it may multiply so fast that it simply crowds out native species. All these things can produce environmental destruction and species extinction.
An introduced species that overgrows in its new habitat is called "invasive." Invasive species include all manner of organisms, from microbes to mammals.
INVASIVE PLANTS
Invasive plants can wreak havoc on entire ecosystems. Gardeners introduced Asia’s water hyacinth
into Florida in the 1880s. It spread throughout the waterways of the Southeast. It clogs streams and rivers. Another harmful invader plant is purple loosestrife.
It is present in every state except Florida. Yet another harmful invader plant is kudzu.
It is present throughout the Southeast.
According to a 1998 survey, more than 20 percent of the protected grasslands in Hungary were infected with invasive plants. The invasive species included common ragweed and Canadian goldenrod.
IMPACT OF WIDER TRAVEL AND TRADE
Human travel and trade greatly increase the problem of invasive species. In some cases, an invasive species is transported deliberately. In other cases, an invasive species is transported by accident. Invasive species may travel as stowaways.
The Louisiana crayfish
was brought to China so that it could be grown in fish farms. But it escaped. It now infests streams in China. Bighead and silver carp
were brought from Asia to be grown in American fish farms. And common and grass carps were brought from Asia to control the growth of aquatic weeds. Asian carp
have severely damaged wetlands in the United States. They have moved up the Mississippi. In 2004, scientists warned that the Asian carp even threatened the Great Lakes.
SCALE OF THE PROBLEM
Environmental studies published in 2004 spread sobering news. The studies said that North America had some 50,000 alien species. About 800 of the species were characterized as invasive.
The reports also noted that invasive species caused economic damage. The losses due to such damage was said to be about $120 billion each year.
The disruptions caused by invaders have given rise to a new field of study. It is called invasive ecology. The disruptions also have prompted educational programs. These programs are aimed at the public and inspectors at airports and seaports. They explain how to curb the spread of invasive species.
Consider this Question:
- What effects have you seen in your environment that were caused by an invasive species? (Think of a specific type of plant, or even an animal, that tends to "take over" an area) Use evidence from the reading to support your claim.