Biology Reference
In-Depth Information
entry even if detected, and (2) resources are inadequate to provide comprehensive
inspection, even were a larger array of alien species targeted for quarantine. In most
jurisdictions, the large volume of arriving goods, passengers, baggage, and vessels
often precludes meaningful quarantine for more than a handful of unintentionally
arriving species. So, current quarantine inspection programs are generally far from
ideal. A more promising approach would be wider application of vector science -
understanding and managing the motives that create the pathways of introduction
and the specific physical means of introduction (or vectors) that transport species
(Carlton and Ruiz, 2005). The benefits of a vector-analytic approach are that it can
simultaneously work to prevent the introduction of multiple species carried by the
same vector and it is likely to be economically efficient by prioritizing those path-
ways and vectors accounting for the greatest numbers of introductions or invasions.
Its intent is to reduce viable transport of all alien species associated with particular
vectors or pathways instead of just a limited list of already-identified invasives.
This approach requires identification and quantification of pathways and vectors as
well as the development of tactical means to limit successful transport by those
means. Vector science is relatively new but its recent application includes treatment
of ballast water and placement of some restrictions on the import of raw logs for
timber. Detailed studies of pathways and vectors are not available for most taxa or
commodities, and much of what commodity data are available sit unpublished in
government files. But much of what understanding is recently available is summa-
rized in Carlton et al. (2003).
Currently, most countries adopt a short list of known invasives that they attempt
to keep from their shores, and most of these are species liable to accidental intro-
duction. These species are almost always pests of agricultural concern and are a
very small subset of all known or potential invasives. Ideally, one would like to be
able to screen any alien species for potential invasiveness and use that information
to decide whether to allow or ban its deliberate importation. Such screening sys-
tems would require a methodology that can reliably identify and exclude most
invasive species, approve most useful or non-threatening species, and limit the
number of instances of uncertain status that require further assessment. Australia
has developed screening protocols to meet these goals for plant and animal intro-
ductions (Bomford and Hart, 1998; Pheloung et al., 1999; Walton et al., 1999;
Bomford, 2003; Bomford and Glover, 2004), and the plant protocol has been
adopted for use in New Zealand with minor modifications (Williams et al., 2002)
and found applicable to a variety of other locations (Gordon et al., 2008). These
protocols are based on assigning numerical scores to a variety of biological traits
for a species, summing the scores across all assessed variables, and using this sum-
mary score to decide whether to allow importation (low scores), prohibition (high
scores), or further assessment (intermediate scores). By use of such a simple sys-
tem, it has been determined in New Zealand that most invasive species of plants can
be kept from entry, most useful non-threatening plants can be allowed safe entry,
and a small proportion of species fall into a narrow numerical zone of uncertainty
that requires further study prior to making a definitive decision. The system is con-
ceptually simple, evidentiarily explicit, and objective, making it transparent to
