Non-native animals in North America are species that have been introduced to the continent by human activity, either intentionally or unintentionally. These animals live outside their natural historical ranges and their presence in North America is a result of human influence rather than natural processes. This distinguishes them from native species, which naturally occur in a particular ecosystem without human intervention.
How Non-Native Animals Arrive
Non-native animals arrive in North America through various pathways, broadly categorized as intentional or accidental introductions. Human activities are responsible for their presence beyond native ranges.
Intentional introductions often occur for specific purposes. Historically, early European explorers and settlers brought domestic animals like pigs and cattle as food sources for new settlements. Livestock management practices, such as free-ranging, sometimes led to these animals establishing wild populations. Other intentional introductions include species brought for the pet trade, where exotic animals are imported and sometimes escape or are released by owners. Animals have also been introduced for sport hunting, such as the Eurasian wild boar, and for pest control or ornamental reasons.
Accidental introductions are equally significant. A common pathway is through global shipping, where organisms can stow away in cargo or ballast water. Ballast water, used to stabilize ships, can carry aquatic organisms, including larvae and adult forms, from one continent to another. Animals also hitchhike on vehicles, trains, planes, or within wood packing materials. Escape from captivity, such as from farms, zoos, or pet owners, also contributes to accidental introductions, allowing non-native animals to establish wild populations.
Prominent Non-Native Species
Several non-native animal species have become well-established across North America, each with a distinct origin story. These animals arrived from various parts of the world and are now prominent features of the continent’s ecosystems.
The Common European Starling (Sturnus vulgaris) is native to Europe and parts of Asia. Its presence in North America dates back to the late 19th century, with a significant introduction occurring in New York City’s Central Park in 1890 and 1891. This release, reportedly driven by a desire to introduce all birds mentioned in Shakespeare’s works, led to the widespread establishment of the species. Similarly, the House Sparrow (Passer domesticus) originated from Eurasia, North Africa, and the Middle East. It was introduced to Brooklyn, New York, in 1851, with further introductions aiding its spread across the continent.
Wild Boar, also known as Feral Hogs (Sus scrofa), are not native to the Americas. Their ancestors were brought to North America from Europe by early explorers and settlers as a food source starting in the 1500s. Subsequent introductions of Eurasian wild boar in the early 1900s for sport hunting further contributed to their populations, leading to hybrids with domestic pigs that had escaped captivity. Nutria (Myocastor coypus), large semi-aquatic rodents, are native to South America. They were brought to North America in the early 20th century, primarily for fur farming, and became established in the wild due to escapes and releases when the fur trade declined.
The Zebra Mussel (Dreissena polymorpha), a small bivalve, is native to Eastern Europe and Western Asia, specifically the Caspian Sea region. It is believed to have arrived in the Great Lakes around 1986 through the discharge of ballast water from commercial cargo ships. The Emerald Ash Borer (Agrilus planipennis), a wood-boring beetle, originates from northeastern Asia, including China and the Russian Far East. This beetle was first detected in North America in 2002 and is thought to have arrived via wood packing materials. The Burmese Python (Python bivittatus) is native to Southeast Asia. These large snakes were introduced to Florida in the 1970s and 1980s primarily through the exotic pet trade, with many escaping or being released by owners.
Ecological and Economic Alterations
The presence of non-native animals in North America leads to significant ecological and economic alterations. These consequences stem from their establishment and interactions within new environments.
Ecologically, non-native species can outcompete native wildlife for essential resources such as food, water, and habitat. They can disrupt existing food webs by preying on native species that have not evolved defenses against them, or by becoming a new food source that alters predator-prey dynamics. Some non-native animals also change physical habitats, such as altering soil composition, increasing erosion, or modifying water flow, which can further stress native ecosystems. The introduction of diseases to native populations, which may lack immunity, is another ecological concern associated with non-native animals.
Economically, the impact of non-native animals is substantial, costing North America at least $1.26 trillion between 1960 and 2017. These costs include damage to agriculture, such as crop destruction and livestock predation, and harm to infrastructure, including clogging pipes or damaging buildings and levees. Industries like agriculture and forestry have incurred significant costs, with the agricultural sector alone facing approximately $527.07 billion in costs from 1960 to 2017. Substantial financial resources are also allocated to management and eradication efforts aimed at controlling non-native animal populations and mitigating their effects.