Biology Reference
In-Depth Information
future invasions is difficult to quantify. Government agencies have instead often
taken a qualitative approach in which risk probabilities at each step (introduction,
establishment, and spread) are qualitatively categorized by a panel of experts as
“high”, “medium”, and “low”. The product of the constituent probabilities for
invasion is then scored as that of the lowest component (Simberloff, 2005).
A similar assessment may be done for species hazard, and the value of the hazard
risk is then multiplied by that for invasion risk to produce an overall assessment
value (Simberloff, 2005).
There are many problems with the approach just outlined, including its vulner-
ability to political tampering, narrowly circumscribed taxonomic ambit, practical
inability to assess every taxon of interest or concern, presumption of safety for
species whose biology is poorly known, and inability to predict consequences for
species not yet introduced anywhere (Simberloff, 2005). Hence, one must be cau-
tious in placing too much confidence in the results of such assessment, and differ-
ent means of assessing invasion impacts may sometimes be preferred (Binimelis
et al., 2007). However, such qualitative assessments still have value. The important
point about consideration of risk is the conceptual framework that it provides in
thinking about how to reduce the future burden of species invasions. Dividing the
invasion process into separate steps allows for clearer thinking about the biological
and human factors operating at each stage and how those factors might be altered
to best reduce invasion probability. This can allow for better decision-making
about when and how to respond to alien species. For example, increased interna-
tional trade increases the risk of introduction of unwanted aliens in a cumulative
fashion. This trend is not likely to change in the near future, so responsible govern-
ments need to recognize the looming future risk and respond with prevention systems
commensurate to the task.
One means of managing the high uncertainties involved in predicting invasive-
ness and costs is the adoption of a precautionary approach. This principle, as con-
cisely put by Perrings et al. (2005), holds that “where the effects of some activity
are uncertain but are potentially both costly and irreversible, society should take
action to limit those effects before the uncertainty is resolved.” The justification for
such an approach is both that the costs of foregoing preventive action are likely to
outweigh the costs of doing so and that the burden of proof for potentially damaging
activities, such as importing alien species, lies with those benefiting from the activi-
ties. Fundamentally, it is a statement that scientific uncertainty should not be
allowed to prevent society from taking action to avoid potential risks (Andow,
2005). It will come as no surprise, however, that the uncertainties involved in under-
standing species invasions allow for plenty of political bickering over relative costs
and benefits. Consequently, although invasion biologists and managers have long
argued for the application of a precautionary approach to alien-species manage-
ment, presumptions about what constitutes precaution, safety, and risk vary tremen-
dously among countries, government agencies, and international treaties (Andow,
2005). In at least one instance, New Zealand's Hazardous Substances and New
Organisms Act of 1996, the precautionary principle has been codified into law
and is discharged by that nation's Environmental Risk Management Authority
