Environment Planet Earth What Is an Invasive Species? By Max Carol Writer Cornell University Max Carol started writing for Treehugger in 2016 while still a student at Cornell University; he has since graduated with a long list of accolades. our editorial process Max Carol Updated October 11, 2018 phototrip / Getty Images Share Twitter Pinterest Email Planet Earth Conservation Weather Outdoors An invasive species is a nonnative organism that causes ecological harm after being introduced to a new environment. Humans are responsible for the spread of a majority of earth's invasive species, often carrying them to different parts of the world on ships. Once they enter a new ecosystem, invasive species can outcompete native organisms for resources like food, especially if they lack natural predators. Some invasive species also carry diseases that kill native organisms, and many will consume native plants and animals. Invasive species can ultimately cause the decline or extinction of native species, decreasing biodiversity in an ecosystem. Damage Caused by Invasive Species Invasive species have cost humans at least $1.4 trillion dollars globally in damages, approximately five percent of the world’s economy. In the United States alone, invasive plants affect over 100 million acres of land each year, and invasive species have contributed to the population declines of 42% of America’s threatened or endangered species. How Invasive Species Migrate While humans are responsible for the introduction of many nonnative species to new habitats, the relocation of organisms is not a recent phenomenon. Species migrations have been affecting ecosystems since life began on earth. Approximately 3 million years ago, the ecosystems of North and South America were forever changed as dozens of genera of animals migrated between the two continents along the newly formed Isthmus of Panama in an event known as the Great American Biotic Interchange. Armadillos, porcupines, and sloths colonized North America, while horses and predators like foxes and bears entered the southern continent. The introduction of these new predators to South America led to the extinction of many mammalian species that lived there, including all 13 native species of ungulates (hoofed mammals). Still, humans have brought invasive species to new environments in previously unmatched capacities. In 1827, European settlers brought wild rabbits (Oryctolagus cuniculus) to Australia to remind them of home. The rabbits reproduced quickly and soon began to kill many native shrubs and trees by consuming their seeds and stripping off their bark. By damaging vegetation, rabbits also decreased the number of food sources for many of the small ground-dwelling mammals that lived in Australia, leading to their extinction. To combat the rabbit infestation, Europeans introduced the red fox (Vulpes vulpes) to Australia in the 1850s, hoping that it would kill a large portion of the rabbits. Instead, it ate native rodents and marsupials, causing declines in native animal populations. Today, many invasive species are still intentionally brought to different parts of the world to serve as pets, and invasive plants like watermilfoil (Myriophyllum) are used as decorations in aquariums. Most Invasive Species Are Introduced Accidentally Most invasive species, however, are introduced accidentally. During the 18th and 19th centuries, European explorers unintentionally carried black rats (Rattus rattus) and brown rats (Rattus norvegicus) on their ships as they visited new lands, eventually introducing the two species to every continent but Antarctica. When introduced to new regions, the rats fed on native birds, mammals, reptiles, and seeds and spread diseases, hurting native plant and animal populations. Rats still cost humans hundreds of millions of dollars in damages every year. Today, there are thousands of invasive species worldwide and approximately 4,300 in the United States alone. Kudzu, one of the worst invasive plants in America, covers at least seven million acres of land in the Southeast United States. Zebra mussels (Dreissena polymorpha) clog pipes and starve out native fish in the Great Lakes and New England. Asian carp, another invasive species, have been outcompeting native fish for resources in at least 23 states since the 1980s. How to Prevent the Spread of Invasive Species The best way to curb the damages of invasive species is to prevent their spread in the first place. Learn to identify the invasive species that affect your community so that you can report them to your local land manager if sighted. Always clean boats before entering new bodies of water, as this will prevent the introduction of invasive species like zebra mussels or watermilfoil to uncontaminated water systems. Avoid purchasing nonnative decorative plants, but if you do, never release them into the wild. For more information on how to prevent the spread of invasive species, check out this video from the Michigan Department of Environmental Quality.