Biology Reference
In-Depth Information
interior plumbing on all quarantined vessels, public education to gain community
and stakeholder support, and monitoring of the treated areas for one year (Bax
et al., 2002). As noted, successful eradication was achieved within one month of
first detection of the incursion, but success was not declared until mussels had
remained undetected for one year. Most eradication operations neither proceed this
quickly nor have a need to because most invasive species lack this mussel's capa-
bilities for explosive growth. But this example demonstrates what may be achieved
by rapid response against difficult odds when such an operation is approached with
commitment and competence. In marking that achievement, Australia's Northern
Territory has set a useful standard against which other jurisdictions may measure
their own response efforts.
Should an invasive alien species be allowed to spread widely, it is usually
impossible - or at best very expensive - to eradicate it. Under these circumstances,
one is faced with the prospect of perpetual control to mitigate the worst effects of
the alien invader. The means of effecting control and mitigating damage will vary
depending on the taxon, habitat, and management goals, but all such efforts need to
be carefully defined, planned, and executed in order to meet those goals. Mechanical
and chemical control methods are the most widely utilized tactical tools, and numer-
ous options are available, their application and effectiveness depending on the target
(examples given in Kraus, 2002a; Wittenberg and Cock, 2005). Although these tactical
methods form the backbone of most control operations, more biologically sophisti-
cated techniques, such as removal of disturbance regimes that promote proliferation
of the pest, or alteration of habitat to remove refugia for invasives or to provide a
competitive edge to natives, can also be used against some invasive pests.
Introduction of natural enemies - either predators or parasites - from a pest's
native range has been a frequently used control option and is termed “classical bio-
control”. Biocontrol has most often been applied against plant or invertebrate pests,
and these efforts have frequently met with some degree of success in controlling the
invasive pest. When properly applied, biocontrol is often the only hope for effecting
large-scale control against many wide-ranging plants and invertebrates, and some
programs have reduced the target species to such low numbers that it no longer acts
as a pest. However, biocontrol programs have also led to unintended disastrous
consequences for non-targeted native wildlife (Howarth, 1990, 1999; Louda et al.,
2002). This has occurred primarily because some released control species proved
to have wide dietary ranges that went unrecognized because of poor (or no) host-
specificity testing prior to their release. Attempts to use biocontrol against verte-
brates have almost always been ineffective because of lack of host specificity in
vertebrate predators and parasites. Use of vertebrates themselves as biocontrol
agents has often been disastrous because most vertebrate predators have broad diets
and do not restrict their dining to the target species. Because early biocontrol efforts
often created unintended impacts on non-target species these programs are now
often conducted with extensive testing prior to release so as to ensure that such col-
lateral impacts do not occur. Nonetheless, monitoring of post-release outcomes
remains insufficient (Simberloff and Stiling, 1996), and there is still scope for
improving the application of this important control tool.
