Environmental Engineering Reference
In-Depth Information
(
Trichosurus vulpecula
), rats (
Rattus rattus, R
.
norvegicus
), house mice (
Mus mus-
culus
), stoats (
Mustela erminea
), weasels (
M
.
nivalis
), and ferrets (
M
.
furo
) prey
on native birds and have been a key factor in driving a large proportion to extinc-
tion and dramatically reducing the abundance of those species that survive. One
strategy for dealing with this problem has been to maintain threatened species on
predator-free off-shore islands. Another approach has involved attempts to create
predator-free 'mainland islands'. On the mainland of New Zealand, eradication
of invasive predators is generally not feasible even over relatively small areas, even
when predator control is combined with predator-proof fencing. This leaves the
two options: control or 'do nothing'.
h ere are many examples of documented benefi ts for native New Zealand bird
species from control of introduced predatory mammals: control of ship rats and
brush-tailed possums led to increased fl edging success and adult population num-
bers of New Zealand pigeon (
Hemiphaga novaeseelandiae
) (Innes
et al
.
2004);
con-
trol of ship rats (
R
.
rattus
) resulted in signifi cantly higher breeding success of New
Zealand pigeon (Clout
et al
. 1995); control of stoats was associated with increased
survival of nestlings and densities of adult bellbirds (
Anthornis melanura
) (Kelly
et al
.
2005); successful breeding of kaka (
Nestor meridionalis
) in an area in which
stoats were trapped compared with in other areas where there was no predator con-
trol (Dilks
et al
.
2003).
Data collected during these control programmes included the number of preda-
tors of diff erent species that were trapped, breeding success and abundance of
important bird species, aspects of responses by vegetation, and economics of the
control operation. h ese studies enabled an evaluation of impacts and increased
knowledge of the ecology of the main elements of the system. Prioritisation, detec-
tion, documentation of change, multi-species approaches, and monitoring of both
the invasive species and the components of the systems that are aff ected by them,
are incorporated into these approaches. h ey also illustrate the need for continuing
commitment.
Several grasses introduced to Australia exemplify invasive species that have both
positive and negative impacts that infl uence attitudes toward them and man-
agement decisions concerning them. Buffel grass (
Cenchrus ciliaris
) was sown
in Australian rangelands as a pasture grass for the cattle industry and to reduce
erosion in arid and semi-arid pastoral country (Humphreys 1967). The species
naturalized widely or expanded its range to suggest it could cover much of the con-
tinent (Humphries
et al
.
1991). Buffel grass is an important introduced pasture
species for the northern Australian cattle industry (Walker and Weston 1990) but
it is now also seen as having deleterious consequences for native species and com-
munities (Griffi n 1993; Low 1997). These consequences include reduced native
plant species richness (Franks 2002; Clarke
et al
.
2005; Jackson 2005) and fuelling
of high intensity, more frequent fi res (Clarke
et al
.
2005). The confl icting inter-
ests surrounding this invasive species, and its advanced stage of invasion, present
