Biology Reference
In-Depth Information
http://www.hear.org/gcw/). Hundreds of thousands of potential pests could make
the future incomparably worse. This is not merely a reflection of the inherent bio-
logical attributes of each potentially invasive species. The invasive-species problem
is at its most fundamental level a consequence of varied human values, decisions,
and actions (Andow, 2005; McNeeley, 2005), including the commonly taken
choice of doing nothing. Adding to scientific knowledge of invasion biology without
acting on that information, however, is a sterile exercise. How, then, is our infor-
mation being used to manage these problems? What prospects are there for
improving our responses?
Solutions
A variety of actions may be taken to lessen the frequency of invasion or to reduce
the negative impacts of particular invasions. Strategically, one may respond to inva-
sive species at any or all of three stages: by preventing their arrival and establish-
ment, by eradicating newly established populations before they expand, or by
mitigating the costs of widespread invasions. Best protection against invasions is had
by employing actions (or “screens”) at all three stages because each screen acts
independently of the others, and their combined protective effect is multiplicative
(Fig. 1.1). Tactical methods useful at each stage should exploit the biological weak-
nesses of each species; hence, they will vary with species and with the particular
environment in which control is being exercised. As a matter of observation and
logic it is cheaper, more effective, and therefore more efficient to control alien
species earlier in the invasion process than later (see, e.g., Naylor, 2000; Touza et al.,
2007). A logical consequence of this is that prevention of introductions is far supe-
rior in terms of effectiveness, efficiency, and resource use than is reacting to invasions
after they occur. Hence, comprehensive quarantine and screening systems to exclude
species entry to new areas should form the foundation for any alien-species mitiga-
tion program. This paradigm has been applied to some agricultural pests, but the
approach is still new and little applied to environmental pests, except in New
Zealand and Australia. Should alien pests breach the quarantine barrier, the most
cost-effective means of mitigation is to discover and eradicate newly established
aliens while populations remain small. If successful, this avoids the large costs of
perpetual control for widespread species. For environmental pests, long-term control
is usually applied only in relatively small areas of especial ecological significance,
making it an inherently limited solution. Important economic pests may elicit
broader treatment. Clearly, avoidance of perpetual management and its attendant
costs is to be preferred, so prevention of species incursions or their rapid identifica-
tion and eradication prior to spread are strategically the most sensible tools of
choice. Their competent application avoids the difficulty and cost of long-term
control operations and the unpredictable hazards attendant upon allowing alien spe-
cies to become established. Nonetheless, no single prevention screen will be 100%
effective, and sensible invasive-species mitigation programs utilize all three
