Scientists propose new classification scheme for invasive species

Triage is a concept that is increasingly infiltrating the hearts and minds of conservationists and conservation researchers around the world. In a world of limited resources, how do we know where to direct our attention?

A group of researchers from across four continents (Australia, Africa, Europe, North America) has described a new sort of classification scheme for understanding the risks to biodiversity on our planet, modeled upon the approach taken by the IUCN Red List. Rather than describing the species most at-risk for extinction, they’re classifying invasive or alien species based on the level of impact they have on the recipient ecosystem. Think of it as an IUCN “Black List.”

“A critical need for invasion biology is the capacity to evaluate, compare, and predict the magnitudes of the impacts of different alien species,” write the researchers, led by Tim M. Blackburn of the Zoological Society of London’s Institute of Zoology, “in order to determine and prioritise appropriate actions where necessary.” Preventing or mitigating the consequences of species invasion is, after all, one of the biggest ongoing expenses from within a limited set of conservation resources.

The reasoning goes that humans aren’t just impacting the world’s biodiversity by driving species to extinction; we’re also moving species beyond their natural geographic ranges, either intentionally, through the trade of exotic pets and livestock, or intentionally, due to shifting climates and the nursery trade, for example. When a so-called “alien” species is introduced into a new ecosystem, its impacts can range from positive to negligible to negative, and when the impact is negative, it can range from minor to severe.

Classifying invasive species according to the magnitude of their harm is a first step towards creating more effective legislation and prioritizing actions more efficiently. The proposal does this by classifying the type of impact that an alien species has, in addition to the severity of that impact: minimal, minor, moderate, major, or massive.

For example, an introduced species could impact an ecosystem by competing for food with a native species, or it could run a native species to extinction due to predation. Alternatively, an introduced species could hybridize with a native one, it could bring foreign diseases and parasites with which native species have not evolved to cope, or it could itself be toxic to native plants and animals. It’s easy to think of the ways in which invasive animals change ecosystems, but plants do it too. For example, S. terebinthifolius is an alien plant species which forms dense thickets in river bottoms, ultimately changing the hydrology systems of invaded freshwater systems. I. cylindrica is a grass that more than doubles the biomass of leaf litter, which significantly increases the risk of fire.


Together, the proposed “Black List” will allow researchers and policymakers to directly compare the broad range of impacts attributable to a tremendous diversity of alien species, which operate at different levels both ecological complexity and geographic scale. It also brings us a step closer to achieving Target 9 of the Convention on Biological Diversity, which states, “by 2020, invasive alien species and pathways are identified and prioritized, priority species are controlled or eradicated, and measures are in place to manage pathways to prevent their introduction and establishment.” – Jason G. Goldman | 7 May 2014

Source: Blackburn TM, Essl F, Evans T, Hulme PE, Jeschke JM, et al. (2014) A Unified Classification of Alien Species Based on the Magnitude of their Environmental Impacts. PLoS Biol 12(5): e1001850. doi:10.1371/journal.pbio.1001850

Header image: The lionfish, one of the most invasive species in the Carribean, via