Thousands of species have been moved by people to areas where they do not naturally occur. These alien species can have negative impacts on the environments into which they are introduced. Given the vast number of aliens, and the broad range of impacts they can have, how do we identify which are the worst in order to prioritise our remedial or preventative actions? One method that shows a lot of promise is the Environmental Impact Classification for Alien Taxa (EICAT). This is a new protocol that has been developed to enable invasion biologists to identify and categorise the magnitude and types of impacts associated with alien taxa, and in so doing, allow clear comparisons to be made regarding the impacts of alien species across different regions and taxonomic groups.
It is possible that EICAT will be formally adopted by the International Union for the Conservation of Nature (IUCN) as their formal mechanism for classifying the impacts of alien species. If this happens, EICAT assessments for all known alien species worldwide should be completed and peer reviewed by 2020, in-line with the requirements stipulated under Aichi Target 9 of the Convention on Biological Diversity (CBD) and Target 5 of the EU 2020 Biodiversity Strategy.
As EICAT is a new protocol, a key step in its development is to apply it to a set of species with alien populations, in order to test how readily it can be used, and to identify any aspects of the protocol that may need refinement. To do this, a team of invasion biologists based at University College London’s Centre for Biodiversity and Environment Research (CBER) and the Stellenbosch University DST-NRF Centre of Excellence for Invasion Biology recently carried out a global assessment of the environmental impacts of alien birds using EICAT.
Alien birds were categorised by the severity (Figure 1) and type (Figure 2) of their environmental impacts. Most impacts were categorised as either Minimal Concern (MC) or Minor (MN), although 37 bird species had moderate (MO) impacts or above, causing declines in the populations of native species. Alien birds were primarily found to impact upon the environment through competition, predation, hybridisation and frugivory (which caused the spread of alien plants). However, impact data were found for only around 30% of alien bird species worldwide, with the rest categorised as Data Deficient (DD).
Figure 1: The number of alien bird impacts assigned to each EICAT impact category. A further 296 species were Data Deficient (DD). MC = Minimal Concern; MN = Minor; MO = Moderate; MR = Major; MV = Massive (Evans et al., 2016).
Figure 2: The number of alien bird impacts assigned to each EICAT impact mechanism. Com = Competition; Pre = Predation; Int = Interaction with other alien species; Hyb = Hybridisation; Gra = Grazing/herbivory/browsing; Dis = Transmission of disease to native species; Che = Chemical impact on ecosystem; Par = Parasitism; Str = Structural impact on ecosystem (Evans et al., 2016).
The study demonstrates that EICAT can be used to categorise and quantify the impacts of alien species for a complete taxonomic class. However, it also indicates that there is much to learn about the impacts of aliens, as we have no information on the environmental impacts of most species, even in a well-studied group like birds. This is perhaps one of the key benefits of EICAT – by facilitating a global stocktake of the impacts of alien taxa, EICAT directs attention not only to the most damaging alien species, but also to those species, locations or impact mechanisms for which we do not have sufficient information from which to make informed management decisions to mitigate the impacts of alien taxa.
Click here to access the paper.