Environmental Engineering Reference
In-Depth Information
However, in this chapter we focus on the tools and techniques available to
exclude, remove, or kill terrestrial vertebrates, or prevent them from breeding, and
explore how this toolkit fi ts the strategic needs of managers (from management at
national borders, to management of established species by containment, eradica-
tion, or sustained control). We touch on obvious gaps in the toolkit, both at these
strategic levels and for critical species, and describe briefl y how they are being
addressed around the world.
Compared with invertebrates or plants, vertebrates have a well-known taxonomy
and are usually large and obvious, making it more diffi cult for them to invade with-
out being detected. Terrestrial vertebrates form a minor proportion of all invasive
species, e.g. only eight of the 283 species that have become invasive in China (Xu
et al
. 2006b). However, their impacts, particularly to biodiversity values, are often
disproportionately high, particularly on islands (Mulongoy
et al
. 2006).
Preventing invasion by vertebrates is easier than for invertebrates simply because
they are larger and therefore less likely to be introduced accidentally, for example,
50% of new vertebrate occurrences in China were intentional compared with just
14% for invertebrates (Xu
et al
. 2006b). h erefore, the main tools to prevent inva-
sion by new terrestrial vertebrates are the laws governing legal importation and
border quarantine aimed at detecting illegal importation. Because it is seldom
possible to prevent all incursions, laws also need to provide for some form of in-
country surveillance and, more importantly, for a rapid response to remove acci-
dental incursions or escapes before the species establishes a population (Chapters 1
and 2, this volume).
Managing the risk of unwanted incursion is easiest for island states (discussed
in other chapters of this volume). Wildlife managers in most countries know what
exotic terrestrial vertebrates are present as domestic, feral, or wild animals within
their borders, although knowledge of which species are in the pet trade is often
incomplete. h ey usually have some idea of which species are not present but may
be particularly undesirable (e.g. Bomford 2003) and include them on a blacklist
or impose conditions on how they may be held (for example, in zoos). h ey have
access to information on the distributions and densities of many species elsewhere
in the world and can make some judgement on whether they are likely to establish
if they arrive or escape (Forsyth and Duncan 2001), and may have some knowledge
of the likely pathway(s) by which the species might arrive. h us the risks and path-
ways of arrival are probably easier to predict for vertebrates than for invertebrates
or weeds, if only because there are fewer species.
h e major risk of vertebrate invasion comes from a few invasive vertebrates that
regularly fi nd their way onto ships and aeroplanes, with the highest risk appear-
ing to be from rodents (
Rattus
spp.,
Mus musculus
), common and jungle mynas
(
Acridotheres tristis
and
A
.
fuscus
), Asian house geckos (
Hemidactylus frenatus
), and
