Biodiversity: Towards a Black List of Invasive Species

Spreading animal and plant species around the globe is one of the most serious environmental changes brought about by humans and it has long-term repercussions: the exotic newcomers can destroy the natural environments of native flora and fauna and thus cause long-term reductions in biological diversity. By setting up a world-wide Black List of invasive species, combatting the worst pests can be prioritised and simplified. The Black List is the result of international collaboration including the Department of Biology of the University of Fribourg.

The developped scheme is adaptive to different invasive animal and plant species, as for example the Muskrat, Giant hogweed, Zebra mussel, Canada goose (Pictures: Thinkstock).

In Europe alone more than 13,000 exotic species are known and in Switzerland there are around 900. These invasive species can cause serious damage in their new environment, for example: the extinction of native organisms, disruption of nutrient and water cycles and alteration of natural disturbance regimes (e.g. fire). The prevention or mitigation of such environmental damage consumes a large proportion of the already scarce resources available for conservation. So it is important to know which invasive species are the most detrimental, both today and into the future (and also which only have a minor impact), in order to design effective regulations for the prevention, elimination and control of invasive species. A general problem in doing this is the question of how one can compare the enormous range of possible types of damage caused by diverse groups of invasive species which can differ significantly in their complexity and in their expansion over time and space.

Success via Comparison

A team of recognised experts from four different continents, in collaboration with the International Union for Conservation of Nature (IUCN), has found a pragmatic solution to this problem: they defined various scenarios of detrimental impacts on native species which are brought about by different mechanisms. The scenarios describe different levels of damage in such a way that increasingly severe categories of damage reflect an increase in the order of magnitude of the detrimental impacts (impacts on native individuals, populations, communities). In this way the level of damage caused by different invasive species and differing mechanisms can be directly compared. An invasive species which is thus assigned to a higher impact category is therefore more damaging to the environment than are species in lower impact categories, regardless of their mechanism.

Well equipped, thanks to the Black List

This scheme makes it possible to rank invasive animal and plant species according to the level of damage they cause and thus to set up a so-called Black List of damaging exotic species In its structure and logic the scheme corresponds to the widely recognised Red List of the IUCN which categorises species threatened with extinction. Similarly to the Red List, the Black List can be used to identify species in urgent need of action, as required by international conventions on threats to biodiversity. So as well as being used as a basis for prioritisation, the List can also be further developed into a formal indicator of progress towards the EU’s Aichi 9 biodiversity targets for the identification and management of high-priority invasive species and their pathways.

This collaborative study has just been published in the renowned scientific journal PLoS Biology.

Link to the study
Blackburn TM et al. (2014) A Unified Classification of Alien Species Based on the Magnitude of their Environmental Impacts. PLoS Biology 12(5): e1001850.

Dr Sven Bacher, Department of Biology, University of Fribourg,, 026 300 88 22