Introduced species

An introduced species is a species transported by human activity beyond its natural range into a new area. It may or may not establish, spread, or cause harm.

Introduction pathway: A route or activity through which organisms are transported beyond their natural ranges. Ships, trade, travel, and releases carry species into new areas.
Native species: A species that occurs in a region through natural processes rather than human introduction. Its presence contrasts with a species transported there by people.
Biosecurity: Measures that prevent harmful biological agents or organisms from entering and spreading. Border controls and risk measures can reduce unintended introductions.
Cane toad in Australia: A population of cane toads introduced to Australia in 1935 to control agricultural pests. Its spread and toxicity illustrate harmful consequences of a deliberate introduction.
Propagule pressure: The number and frequency of organisms introduced to a new area. Repeated arrivals and larger introductions increase the chance of establishment.
Natural range expansion: The movement of a species into new areas through its own dispersal or environmental change. It distinguishes natural colonization from human-mediated introduction.
Ballast water: Water carried in ships to maintain stability, which can transport aquatic organisms between ports. Its movement is a major maritime pathway for aquatic introductions.
European starling in North America: The North American population descended from European starlings released in New York City in 1890 and 1891. It exemplifies a deliberate introduction that became a widespread population.
Biological establishment: The formation of a self-sustaining population by organisms in a new area. Arrival alone does not make an introduced species persistent.
Naturalized species: An introduced species that maintains a self-sustaining population in its new area. Naturalization is a possible outcome after introduction, not a synonym for arrival.

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