A novel system for ranking and comparing the impacts of alien species

04 October 2017

By Dr Sabrina Kumschick (SANBI biological invasions scientist)

SabrinaIt seems to be part of human nature to rate things against each other, to rank and compare, and make lists of the “best” and the “worst”. Systems have been developed for example to rank soccer teams according to their performance; cities and countries around the world are ranked according to living standards and happiness.

Many of the lists and rankings out there are based on purely on peoples’ opinions (for example “The 10 most beautiful holiday destinations”), but others, like the examples mentioned above, consider a transparent set of factors with various levels based on well-defined criteria.

Because many alien species pose a global threat to human well-being and livelihoods, researchers have now developed a transparent ranking system for plants and animals moved around the globe by humans to find out which are the worst. Their study was published in the journal Methods in Ecology and Evolution.

Alien species can cause harm in many ways in areas to which they are introduced. Besides the effects on biodiversity, which can lead to extinctions of native species and transformations of whole landscapes and ecosystems, they can also have wide-ranging effects on human health, livelihoods, and well-being. For example, the Tiger Mosquito (Aedes albopictus), which is originally from South-East Asia, is spreading devastating diseases like Dengue and yellow fever, and is therefore considered a significant threat to human well-being in many countries around the world.

It is not only diseases and insects which are problematic to humans. The Cane Toad (Rhinella marina) for example, which was first introduced to Australia to control a crop pest, has subsequently gotten out of control and has spread over large areas.

This is causing major problems for the indigenous people as they can no longer practice certain traditions like bush meat hunting due to the lack of prey caused by this invader, and their well-being and livelihoods are therefore greatly affected. Such impacts on human livelihoods and well-being have received little attention to date, or they are underrated in a world where everything’s worth is rated based on its monetary value.

“We acknowledge that money does not equal human happiness and well-being, and does not have the same meaning everywhere in the world” says Sven Bacher, professor of ecology at the University of Fribourg and lead author of the study published in the journal Methods in Ecology and Evolution.

Borrowing a Nobel prize-winning approach from welfare economics, an international team of 17 scientists from three continents proposes a new Socio-Economic Classification of Alien Taxa (SEICAT for short). Bacher explains: “The system classifies alien species on how they affect what people are able to do in their lives, namely their capabilities.” Assuming that what people do in their lives represents their preferred choices of all their opportunities, SEICAT uses the magnitude of changes in people’s activities for classification on a 5-point scale, from Minimal Concern (no changes in activities) to Massive (irreversible disappearance of an activity from a region).

“By focusing on changes in peoples’ activities, SEICAT captures impacts of alien species on human well-being that systems based on monetary values cannot”, explains Sabrina Kumschick from Stellenbosch University and SANBI and senior author on the paper. Impacts on all constituents of human well-being, such as health, material assets, safety, and social and cultural relationships are measured at the same scale thus allowing impacts of different species to be compared and ranked.

In contrast to monetary approaches, SEICAT assessments can be made even when data are scarce. It thus allows ranking large numbers of alien species in a relatively short time to find out which are the worst.

This novel tool for comparing and ranking alien species according to their effects on human well-being and livelihood can also be used to underpin decisions on which species to spend resources on when it comes to management. “Such insights are crucial in an age when managers simply cannot afford to tackle all invasive species” says Dave Richardson, Director of the Centre for Invasion Biology, a co-author of the paper.

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