Invasive alien species are animals, plants, fungi or microorganisms introduced into natural environments outside their natural range, most often (intentionally or unintentionally) by humans. In these new areas, they have established themselves, reproduced, and spread. These species have a negative impact on native biodiversity, ecosystem functions, economic activities, as well as human health and quality of life. Due to their ability to spread and adapt quickly to new environments, they can displace native species, alter habitats, and cause serious ecological consequences. The problems they cause, and the risk of their spread are rapidly increasing due to the rise of global trade, transportation, tourism, and general mobility. With the expected climate changes, this issue is becoming even more urgent.
The different ways through which alien species colonize new environments are called pathways of introduction. Some species were intentionally introduced by humans (for hunting and fishing, biological pest control, or as ornamental plants), while others are unintentionally introduced through the transport of contaminated materials (seeds, soil, wood, food) or as stowaways (in various vehicles, ships, airplanes, construction machinery, clothing, footwear, or human equipment, and through the ballast water of ships). For alien species kept in captivity (botanical and zoological gardens, fur farms, pets, aquarium or terrarium species), there is the possibility of their escape or release into the wild. Corridors (tunnels, connections between river basins or seas) can also unintentionally facilitate the crossing of previously impassable geographic barriers for alien species. Once alien species are established in an area, they can spread to new locations without human help, through natural dispersal via seeds, vegetative growth, or, in the case of animals, by their own movement.
