Where is the best place to live? What is the happiest nation? Which country has the most suicides? Rankings and comparisons of every kind are very popular. Under the leadership of Sven Bacher, professor of biology at the University of Fribourg, scientists have now developed a classification system to determine which introduced species makes life most difficult for humans.

"Invasive species introduced by humans can cause considerable damage in their new habitat. In addition to the impact on biodiversity from the extinction of native species to the destruction of entire areas and ecosystems, introduced species may also seriously compromise human well-being, health and livelihood", said Professor Tim Blackburn, Chair of Invasion Biology at UCL. For example, the Tiger Mosquito (Aedes albopictus), which is originally from South-East Asia, spreads diseases such as dengue fever. In many countries around the world it is considered a major threat to human health.

However, it is not only diseases and insects which are a problem for humans. The Cane Toad (Rhinella marina), for instance, which was originally introduced to Australia to exterminate certain pests, has gradually grown out of control and has spread extensively. This has subsequently led to problems for the indigenous population as they can no longer continue certain traditions such as bush meat hunting due to the lack of prey caused by the Cane Toad.

Not a monetary approach

To date such effects on human livelihoods and well-being have either received little attention or have been underestimated as the financial damage they cause is not sufficiently remarkable. Under the leadership of Sven Bacher, professor for biology at the University of Fribourg, an international team of 22 scientists has developed a new Socio-Economic Impact Classification of Alien Taxa (SEICAT). As Sven Bacher explains: “The system classifies introduced species by how they affect what people are able to do in their lives, namely their capabilities.” SEICAT is based on a 5-point scale and is intended to assess the degree to which certain activities or habits are limited due to an introduced species.

By focusing on changes in people’s activities, SEICAT also captures the impact of introduced species on human well-being that would be overlooked by a purely monetary approach. The effects on human well-being, whether health, material assets, safety and social or cultural needs are all measured in SEICAT using the same scale or “currency”, therefore enabling a direct comparison and classification to be made. Compared with monetary approaches, SEICAT does not require large amounts of data, making it possible to rank the worst introduced species in a short timeframe.

This new tool for comparing introduced species according to their effects on human well-being and livelihood may also be useful when deciding which species should be controlled as financial and logistical constraints make it impossible to tackle all introduced species.