Assessing the ecological impact of alien species
The Norwegian Biodiversity Information Centre is responsible for evaluating the ecological impacts that alien species may have on native species and nature types.
In conjunction with the 2012 assessment of alien species in Norway, researchers developed a new methodology to assess ecological impact.
While the method is tailored to Norway, it can easily be adapted to other countries. There is an international need for a quantifiable, uniform approach to classifying and assessing alien species and the Norwegian approach may contribute.
Nine criteria, five impact categories
The new method allows experts to evaluate an alien species against nine criteria. Three criteria relate to the species’ invasion potential, or how well it establishes itself and spreads, while the remaining six criteria address the species’ ecological effect.
The values from the assessment allow researchers to assign the species to one of five risk categories:
- Species with severe impact (SE) are actually or potentially ecologically harmful species and have the potential to become established across large areas.
- Species with high impact (HI) have either a restricted/moderate ability to spread, but cause at least a medium ecological effect, or alternatively only a minor ecological effect but have a high invasion potential.
- Potentially high impact (PH) species have either high ecological effects combined with a low invasion potential, or a high invasion potential without any known ecological effect.
- Low impact (LO) species have no substantial invasion potential and ecological effect.
- Species with no known impact (NK) are not known to have spread and have no known ecological effects.
The complete details of the approach have been documented in Sandvik, H., Sæther, B.-E., Holmern, T., Tufto, J., Engen, S. & Roy, H. 2013. Towards a generic ecological impact assessment of alien species in Norway: a semi-quantitative set of criteria. – Biodiversity and Conservation 22 (1): 37-62.
Briefly, the method is based on documented, verifiable data that includes the following species-specific information:
- Expected population lifetime, or how well an alien species will persist in its new environment
- Expansion rate, or how fast a species will populate an area
- Projected area of habitat types the species can occupy
- Effects on native species, both threatened or otherwise
- Effects on habitat types, both threatened or otherwise
- The ability of a species to transmit its genes to native species
- The ability of a species to transmit parasites or pathogens
This information allows researchers to plot the risks posed by each species on two axes, one of which shows the species' likelihood of establishment, spread and dispersal (its invasion potential), while the other shows the degree to which the alien species will interact with native species or transform habitats (its ecological impact potential).
The development of the new methodology was spearheaded by Professor Bernt-Erik Sæther and Dr. Hanno Sandvik at the Norwegian University of Science and Technology’s Centre for Conservation Biology (CCB, now the Centre for Biodiversity Dynamics, CBD).
It was fine-tuned in cooperation with a coalition of researchers from different institutions in Norway and staff from the Norwegian Biodiversity Information Centre.
The methodology provides an objective classification of the species' potential impact on the Norwegian environment. The researchers relied on much of the same principles that were used in the preparation of ‘The 2010 Norwegian Red List for Species”.
The criteria are applicable to all multicellular species regardless of taxonomic position.