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What are Invasive species?

Find out more about invasive species and why they threaten our world.

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Ecology and Management of Invasive Alien Species: Management


The most common approach for prevention of invasive organisms is to target individual species. However, a more comprehensive approach is to identify major pathways that lead to harmful invasions and manage the risks associated with these. Although international trade and travel are believed to be the leading cause of harmful unintentional introductions, there is no detailed knowledge base on the actual pathways, except in very few countries. Exclusion methods based on pathways rather than individual species should be a more efficient way to concentrate efforts where pests are most likely to enter national boundaries and avoid wasting resources elsewhere. Moreover, it identifies more species, including more false negatives of the common approach, and identifies more vectors, pathway systems, and underlying introduction mechanisms. Risk assessments can be done for pathways as well as individual species.

Many introduced species are economically important species for agriculture.Most of the current prevention measures target certain species known to be pests in the country or elsewhere. However, these species are predominantly economically important species for the agricultural, forestry, or human health sectors. Prevention of species on these "black lists" is the rather conservative goal for quarantine and other measures taken at present. A more recent approach in order to incorporate all potentially dangerous organisms, not only in an economic view but also in terms of saving the world’s biodiversity, is a move to using "white lists". The approach is often also called "guilty until proven innocent". A proposed intermediate step is the use of "pied lists", favoured for specific reasons.

The brown tree snake, Boiga irregularis.The most reliable method for predicting a species’ invasiveness, is to extrapolate from its record as an invasive species under similar conditions elsewhere (Case Study 3.23 "Invasiveness Cannot Be Reliably Predicted"). Species known to be invasive elsewhere must be considered high priority black list species, like the brown tree snake is for Hawaii. The "pied list" would contain a section of known pest species (equivalent to black lists) with strict regulations and measures to ensure pest-free imports. Another section of the list would describe species cleared for introduction (white lists) - organisms declared as safe. All species not listed are regarded as potential threats to biodiversity, ecosystems, or economy. A stakeholder proposing an intentional introduction has to prove the safety of the species in a risk assessment process before introduction. Species assessed for their likely invasiveness would be added to the white or black list depending on the outcome of the investigation. However, since invasiveness of alien species can vary with time, genetic composition of the introduced population, and changes in human behaviour (e.g. in land use), the species on the white lists have to be re-assessed in appropriate intervals, e.g. environmentally benign species can become invasives.

Exclusion methods would then entail:

  • Quarantine laws and regulations

  • Accessibility of information on invasive organisms

  • Public education

  • Inspection

  • Treatment technologies for pathways to prevent bio-invasions

It should be stressed at this point that education is a key component of successful prevention and management methods. The public has to be informed why prevention measures are taken and what impact failure can cause. The public as well as the companies concerned should perceive prevention measures not as arbitrary nuisance but rather as necessary aspects of travel and trade to care for the future commercial and natural environment.