Environmental Engineering Reference
In-Depth Information
of control and the target: the stronger and more specifi c the control, the greater the
effect (Caut
et al
. 2007).
Removal of superior competitor: when the inferior competitor is not con-
•
trolled at the same time, its population reaches carrying capacity.
Superior competitor is controlled, but not eradicated: the inferior competitor
•
population here again increases its population through a competitor release
process.
Simultaneous control of both competitors: the inferior competitor increases
•
when the indirect positive effect (removal of the superior competitor) exceeds
the direct negative effect (its own removal). This occurs when the control
effort is high and either the control specifi city is high or the intensity of com-
petition is high (Caut
et al
. 2007).
15.3.3.4 Post-eradication monitoring
Post-eradication monitoring will provide information on the eradication success,
both in terms of complete elimination of the target species and of the recovery of
the invaded ecosystem (Blossey 1999). A good example of the utility of such mon-
itoring is given by a recent study where it allowed the monitoring of the recovery
of a native species (Pascal
et al
. 2005). Post-eradication monitoring will also enable
managers to catch unanticipated side effects, or know whether and when to imple-
ment contingency plans for dealing with undesired outcomes (Mack and Lonsdale
2002; Zavaleta 2002).
h e information collected during pre- and post- monitoring allows us to:
•
Contribute information to a knowledge base on effects of alien removal in an
ecosystem context that better prepares us for future control and eradication
programmes.
Learn about the impacts of alien species on both alien and native components
•
of the biota—information that is crucial to the determination of whether eco-
system restoration is likely to be achieved.
Provide vital impact evidence that will help to support future eradication
•
campaigns. As rightly claimed by Towns and colleagues (2006), 'With well-
conceived projects that include rigorous measurement of the responses to rat
eradications, it may be possible to generate models of rat effects for a range of
species and locations. Without such models, the motives and justifi cation for
rat eradications will continue to be questioned'.
Also, it is important—when logistically possible—to couple pre- and post mon-
itoring with a comparison to another island that is free of the alien species: the
before-after control-impact (BACI) protocol. h is protocol is used to assess the
impact of an event on variables that measure the state of an ecosystem. h e design
involves repeated measures over time, made at one or more control sites and one
or more impacted sites, both before and after the time of the event that may cause
an impact (Manly 2000).
