On a global basis, alien species are listed among the greatest threats against biodiversity, but what is an alien species?
- Regionally alien species
Alien species are species that occur outside their natural range and dispersal potential. Alien species are spread by human activity, intended or unintended, to new areas.
Alien species do also include taxa below species level such as subspecies, varieties, cultivars and hybrids. The term alien species includes all life stages that might survive and subsequently reproduce, i.e. seeds, eggs, spores or other biological material.
Regionally alien species
The risk assessment covers species that are alien to Norway. In addition, the possibility exists to risk assess regionally alien species.
Regionally alien species are species native to Norway, that have been introduced to novel areas within Norway by humans after year 1800. Occurrences in the species’ natural range (extent of occurrence, past or present) are referred to as regionally native; occurrences outside these species’ natural range and dispersal potential are referred to as regionally alien. For example, the fish species Rutilus rutilus naturally belong in South-Eastern Norway, but have been introduced into fishing waters in Central Norway. Rutilus rutilus is therefore considered a regionally alien species in Central Norway.