Environmental Engineering Reference
In-Depth Information
15.3.3.1 Hyperpredation
Control options for cases where hyperpredation is likely include:
No control: the alien predator population will remain large mainly due to the
•
presence of alien prey, and the native prey population will go extinct with time
due to cat predation.
Control of alien predators only: the presence of alien prey precludes the
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eradication of predators, allowing only a partial recovery of the native prey
population.
Simultaneous control of both aliens: for the same control effort as above,
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eradication of alien prey helps achieving the predator extinction, allowing
total recovery of the native prey population.
It is important to note that if the control of the introduced prey is not su
cient,
the native prey may be destroyed, even if the predator population is being con-
trolled. h us, the control eff ort is a critical factor contributing to the success of a
programme: control eff ort must be above the intrinsic growth rates of both intro-
duced species (Courchamp
et al
. 1999b). h ese parameters should be obtained
during pre-eradication studies so that the required timing and control eff orts can
be established.
15.3.3.2 Mesopredator release
The hyperpredation process has already highlighted the importance of controlling
both introduced predator and prey species; however, the level of control is crucial
to avoid mesopredator release in systems containing native prey (e.g. bird, lizard),
introduced mesopredator (e.g. rats), and introduced superpredator (e.g. cat):
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High superpredator and low mesopredator control effort: when the super-
predator disappears the native prey may go to extinction through mesopreda-
tor release.
Low superpredator and high mesopredator control effort: this combination
•
of control will enable the survival of the prey population, although it should
be noted that sometimes a very low number of superpredators can lead a prey
population to extinction (Vazquez-Dominguez
et al
. 2004).
High control effort for both predators must be regarded as a potentially good
•
option, provided the timing and forces are set according to the specifi cities of
the ecosystem of concern.
h e fate of the native prey species will depend on the superpredator control level;
the prey will disappear if this control level is too high (Courchamp
et al
. 1999a).
15.3.3.3 Competitor release
Assuming both competitors are controlled by a common, non-specifi c method,
the extent of the competitor release process is directly infl uenced by both the levels
