Environmental Engineering Reference
In-Depth Information
the 'all at risk' condition (Liebhold and Bascompte 2003). It also implies the
funds are available to achieve the rule.
There is no immigration of individuals that can breed.
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•
There must be no net adverse effects. Eradication may not be desirable if the
adverse affects on non-target species of the control methods available are pre-
dicted to be unacceptable and unresolvable, or if the consequences of removal
of the pest outweigh the benefi ts (Courchamp
et al
. 2003).
Non-target problems are generally manageable either by changing the control
method (e.g. toxic baits to eradicate ship rats (
Rattus rattus
) on Middle Island were
presented in bait stations that excluded the native bandicoots (
Isoodon auratus bar-
rowensis
) (Morris 2002), or by temporarily taking some or all of the non-target
populations to a safe place (e.g. protection of the endemic deer mice (
Peromyscus
maniculatus anacapae
) during Norway rat (
Rattus norvegicus
) eradication on
Anacapa Island (Howald
et al
. 2003).
Predicting and managing adverse eff ects that result from the removal of the
pest(s) is one area that requires further consideration. Removing one pest may
lead to an increase in another pest. h is may be unexpected, e.g. the eruption
of the exotic vine
Operculina ventricosa
following eradication of feral goats and
pigs on Sarigan Island (Kessler 2002). However, some eff ects are predictable,
and certainly can be tested experimentally before the eradication is conducted.
For example, the eradication of feral goats from Guadalupe Island, Mexico has
resulted in an increase the biomass of both native plants and in exotic grasses.
h e latter has caused an increase in abundance of mice (
Mus musculus
) and
probably of feral cats (
Felis catus
) with potential consequences for native biota.
h e increase in grass biomass has also increased the risk of fi re with potential
consequences for the regenerating relict stands of the endemic
Pinus radiata
guadalupensis
(A. Aguirre pers. comm.). h ese consequences are manageable
(eradicate the mice and cats, and plant the pines in widely dispersed parts of
the island), but it raises the question of the order in which pest species should
be eradicated.
h e range of other issues that may also have to be considered in a feasibility plan
may constrain conformity to one or more of these criteria. For example, eradica-
tion was not practical for Himalayan thar (
Hemitragus jemlahicus
) in New Zealand
because of intractable objections by some landowners (Hughey and Parkes 1996).
Not all thar could be put at risk, so the rate of removal and immigration criteria
could not be met. Attempts at eradicating hedgehogs (
Erinaceus europaeus
) over
a range of about 50,000 ha on the Uist islands, Scotland, also appear unlikely to
succeed because animal welfare groups have limited control intervention to a short
annual period when the females are active but not lactating (Warwick
et al
. 2006),
thereby increasing the likelihood that the rate of removal (without heroic eff orts)
will not exceed the annual rate of increase.
Feasibility of eradication must therefore be viewed in the context of the minimum
eff ort that can be mustered to meet the obligate rules and overcome constraints
