From CopperWikiWhen the small brown snake entered the U.S. Pacific Island Territory of Guam, there were 13 species of birds, 12 species of lizards and one bat species. What remains is one bat species, three forest birds and six native lizard species. On the other hand there are now one million nocturnal brown snakes even in the smallest areas of Guam. They damage power lines and enter homes through bathroom vents. The small brown snakes belong to the invasive species.
 A Major Threat to Native Species
Invasive species, which can be plants, animals, and other organisms (e.g., microbes), occur as a result of human activities and displace native species, disrupt ecosystems, and harm recreational activities such as fishing, boating, and hiking. They not only represent a major threat to native species but also damage commercial, agricultural, and aqua-cultural resources. These species cause damage to the lands and waters that native plants and animals need to survive. Worldwide these species are estimated to have caused damage worth $1.4 trillion – five percent of the global economy.
In the first global analysis of invasions in aquatic habitats carried out in over 1000 river basins, it was found that there was direct relation between species invasion and gross domestic product, higher human population density, and nearby urbanized land. As economic expansions are continuously on the rise globally, this is a cause for grave concern.
 Risk to Endangered Species
According to the U.S. Department of Agriculture (USDA), about 42% of the species on the Threatened or Endangered species lists are at risk primarily because of alien-invasive species. In other regions of the world this figure is as high as 80 percent. These species are seen to appear in areas where economic activity is high. The United Nations has published an interesting map that shows the major pathways and origins of invasive species infestations in the marine environment across the world. 
 The US Example
It is estimated that in the history of the United States 50,000 non-native species have been introduced which now provide more than 98% of the country’s food system. They include corn, wheat, rice, and other food crops, and cattle, poultry, and other livestock. Over and above these, a number of exotic species have been introduced for landscape restoration, biological pest control, sport, pets, and food processing. Many of these non-native species have caused tremendous harm to the environment and the economy of the country.
Most alien plants established in the US were for food, fiber or ornamental purposes. Many of the 20 species of mammals introduced in the US, including dogs, cats, horses, burros, cattle, sheep, pigs, goats, and deer, had escaped or were released in the wild, and have subsequently become pests by preying on native animals, grazing on vegetation, or intensifying soil erosion. Some of the rodents introduced have become serious pests on farms, in industries, and in homes.
 Damage to Marine Ecosystems
Marine ecosystems around the world have been damaged by the entry of invasive species in ports, coastal areas, and watersheds and pose the biggest threat to coastal environments. Invasive species can persist and spread like many forms of pollutions which degrade over time.
 Global Trade in Marine Organisms
In the course of business non-native species are raised and sold by live fish and shellfish importers, aquaculture facilities and retail pet stores. Along the way specimens can escape, and unknowingly serve as a vector for the introduction of other organisms. Organisms may also introduce non-native species are also introduced into new environments in the course of transportation of living organisms.
Ships can control the introduction of invasive species by exchanging ballast water in the middle of the ocean. This would reduce the risk of transferring organisms from one ecosystem to another.
 Encroaching Upon Rainforests
In our focus on how the climate is affecting our ecosystem, we tend to ignore how non-native trees are encroaching upon rainforests. Being more aggressive, these invasive species change the natural ecological structure of the rainforests.
A research team from the Carnegie Institution’s Department of Global Ecology used new remote sensing technology on aircraft to survey an area more than 220,000 hectares (850 square miles) in size of Hawaiian rain forests. Invasive species are not new to the Hawaiian Islands. Livestock, which the very first human settlers brought with them, stripped the island of its vegetation. Later the Europeans brought the black rat, a dreaded predator in island ecosystems that has helped decimate bird populations in Hawaii.
Hawaiian rainforests help soak up carbon that would otherwise be in the atmosphere, but these invasive species change the amount of carbon stored in ecosystems.
 Some Examples of Invasive Species
- Hydrilla -- A rapidly growing plant that thrives in water and is often confused with waterweeds. Native of Africa, it was brought to the US as an aquarium plant and has since spread to many states.
- VHS -- Viral Hemorrhagic Septicemia (VHS) is a deadly fish virus and an invasive species
- Spiny Waterflea and Fishhook Waterflea -- They are predators and can be transported by fishing boats to newer water bodies
- Emerald Ash Borer -- An exotic insect, native to Asia. It attacks both stressed and healthy ash trees, typically killing its host in one to three years.
- Mustela nivalis (mammal) -- These are voracious predators and appear mostly in agricultural areas, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, tundra, urban areas
- Rubus niveus (shrub) -- A shrub native to Asia that may form dense, impenetrable, thorny thickets that can displace native species
- Bromus inermis (grass) -- Occurs on roadsides, riverbanks, edges of fields, and in woods and pastures. It prefers sandy soils to silty ones
- Oxycaryum cubense (aquatic plant, sedge) -- Wetland sedge found throughout the Americas and in parts of Africa. It forms large floating mats on standing water and may be aggressive and invasive in some areas.
 What We Can Do
In order to protect native plants and animals it is vital that we take steps to control and eradicate invasive species. Once the invasive species enter the ecosystem controlling them becomes increasingly difficult. Prevention and early detection are the most cost-effective strategies to combat these species.
Some of these are:
- Make sure you are not buying invasive plants for your garden. Take the help of nursery staff to identify invasive plants
- Clean your boat thoroughly if you are planning to move to a different water body to avoid hitchhiking weed seeds and pathogens.
- Keep your bags clean when you travel from one place to the other as fruits and vegetables, plants, insects and animals can carry pests or become invasive themselves.
- Don't release aquarium fish and plants, live bait or other exotic animals into the wild.
- Help remove invasive species from your local park or any nearby wild areas. Help educate others about the threat.
- Control invasive plants by cutting off their water supply. We can also make use of fire, bio-controls (e.g. natural predators), and judicious applications of herbicides, flooding, or other methods.
- ↑ 
 See Also
- Protecting Native Plants and Animals
- Trees are Trees Worst Nightmare
- Freshwater Fish Invasions The Result Of Human Activity
- Update on the environmental and economic costs associated with alien-invasive species in the United States
- Preventing the Spread of Invasive Species
- The 5 Worst Invasive Species in the World