Species alien status

The alien status of a species is the second essential variable that an invasion monitoring system needs to deliver. Alien status provides information on whether a species is indigenous or non-native (alien) at any particular locality in which it is found. Information on the natural geographic range of a species provides important baseline information for determining if an alien species is inside or outside of its indigenous geographic range. Alien status information is also essential for designing appropriate policy and management responses.

Deciding if a species is alien (i.e. non-native, exotic or non-indigenous) in a country or whether it is indigenous (or native) to the country, or to parts of the country, is not always straightforward [1]. There are four situations where making the decision about whether a species is alien or not at a particular site can be difficult:

  • The native range of the species is unknown.
  • The range of the species is naturally highly dynamic or shifting in response to climate change [2, 3].
  • There is evidence that the species can evolve quite rapidly once newly introduced to a region, which can blur the signal of its origin and trigger debate about its alien status.
  • The country geopolitical borders do not overlap with biogeographical borders or species range edges. A species can be indigenous to one part of the country and alien to another. However, country boundaries are still relevant to decision-making about alien status because this is the level at which policy and regulations are developed and implemented.

There are a number of resources that can be helpful for finding information about the alien status of a species (whether it is indigenous/native or introduced/alien in an area; see Organisations & Resources).

Relationship between species alien status and Essential Biodiversity Variables.

The status of a species as either alien or native at any particular locality can be considered to be an attribute of the species occurrence variable, i.e. information that is ancillary to species occurrence. It is not itself an Essential Biodiversity Variable (EBV)[4]. Nonetheless, in the context of biological invasions, this information takes on a special significance. It is the essential basis upon which appropriate policy and management decisions are taken. There is also the need to prioritize collection and collation of these data, which are currently inadequate [1], to support effective invasion management.

Referenced material and links

[1] McGeoch, M.A., Spear, D., Kleynhans, E.J.and Marais, E. (2012) Uncertainty in invasive alien species listing. Ecological Applications 22, 959-971. doi: 10.1890/11-1252.1.

[2] Chown, S. L. et al., (2015) Biological invasions, climate change and genomics. Evolutionary Applications. doi:10.1111/eva.12234.

[3]McGeoch, M.A., Latombe, G. (2016), Characterizing common and range expanding species. Journal of Biogeography., 43: 217–228. doi:10.1111/jbi.12642

[4] Pereira, H. M. et al., (2013) Essential Biodiversity Variables. Science 339, 277–278. doi: 10.1126/science.1229931.