Environmental Engineering Reference
In-Depth Information
h e aim of this chapter is to illustrate the importance of considering ecological
interactions between species (including those between invasive species) when
planning a sequence of management actions in either natural or modifi ed eco-
systems. Diff erent types of species interactions are discussed in the following sec-
tions, particularly with respect to the community and ecological dynamics that are
behind these interactions and how this knowledge can be used by managers and
researchers to reduce the likelihood of unexpected or unwanted outcomes in the
management of invasive species. Most studies investigating the impacts of species
interactions have looked at invasive mammalian species on island ecosystems, so
the case studies presented refl ect this bias. h e case studies are used to demonstrate
key principles regarding invasive species interactions and the ways in which they
can be managed successfully. h e main tools and techniques that can aid in the
successful management of an invaded ecosystem are also discussed.
lead to ecosystem recovery
Instances exist whereby an alien species has been present in an ecosystem for suf-
fi cient time that it dominates or has replaced native species and habitats. In some
cases, this can lead to positive association between a native and alien species, thus
further complicating the management of invaded ecosystems. In such instances,
consideration must be given to how the removal of such an invader could in fact
remove an ecosystem function necessary to the survival of other (perhaps threat-
ened) biota (Zavaleta
et al
. 2001). For example, Carter and Bright (2002) describe
how the exotic but non-invasive Japanese red cedar (
Cryptomeria japonica
) plan-
tations on Mauritius provide refuges for native birds against predation by intro-
duced macaques (
Macaca fascicularis
). Given that nest predation by macaques is
signifi cantly lower in cedar than in native forest, the removal of the Japanese red
cedar would indirectly increase the impacts of another alien species (macaques)
on endemics with high conservation value (Carter and Bright 2002). Another
example concerns alien pollinators or seed dispersers that have become the most
important source of pollination or dispersal following the loss of native ones. In
instances where an alien species is non-invasive, its removal may not be of signifi -
cant benefi t to the ecosystem.
There are instances whereby alien plants have indirect negative effects on a native
species even after the removal of the exotic ones (Zavaleta 2002). For example, the
invasive species from the genus
Tamarix,
and the iceplant (
Mesembryanthemum
crystallinum
) have been shown at some sites to salinize soil to such an extent that
native organisms are not able to recolonize after their removal (Vivrette and Muller
1977; El-Ghareeb 1991; Bush and Smith 1995; Shafroth
et al
. 1995).
