Environmental Engineering Reference
In-Depth Information
detection than the other studies. It is possible that
bighorn sheep existed mostly in metapopulations but
that human disturbance has accelerated extinction
rates, and that extant bighorn sheep (meta)popula-
tions now occur in a non-equilibrium state. The results
of this study also indicate that many restoration
projects in the past probably suffered from poor proce-
dures. Many prior translocations consisted of small
founder groups (typically fewer than 25 animals)
released into small, isolated patches of habitat, proba-
bly representing a near-perfect prescription for failure.
tion and elimination, or reduction to a suffi cient level,
of previous causes of population decline and/or
habitat transformation should take top priority. In a
habitat suitability study for an otter reintroduction
project in Utah, United States, it was found that 94%
of the studied streams were unacceptable for reintro-
ductions. Escape cover was the most limiting habitat
attribute, whereas food for the otters appeared to be
available in adequate quantities (Bich 1988). This
study, therefore, led to the recommendation that no
otter reintroductions should be made until riparian
zones were rehabilitated and protected, since re-
establishment of stream-bank vegetation was deemed
essential to provide escape cover for the reintroduced
animals. Similarly, Howells and Edwards-Jones (1997)
studied the feasibility of reintroducing wild boar ( Sus
scrofa ) to Scotland through an assessment of suitable
woodland habitats that could support a minimum
viable population of the target animal. This species
had already been the focus of earlier attempts to
restore the extinct species and to reintroduce it into
Britain (Howells & Edwards-Jones 1997). Based on a
review of wild boar ecology, the authors identifi ed
woodland habitats suitable for supporting the species.
Only long-established woodlands containing some
stands of seminatural origin and larger than 500 ha in
size were considered. None of the woodlands were
deemed optimum habitat for wild boar and none was
large enough to support a minimum viable population
of 300 animals. The study concluded that the goal of
re-establishing a self-sustaining population of wild
boar in Scotland was unrealistic in the short term and
reintroduction did not take place. Habitat destruction
and modifi cation can also be caused by invasive organ-
isms. Such invasions often result in dramatic changes
in ecosystem structure or function (Gordon 1998 ;
Hobbs & Mooney 1998 ). Invasive species may not
only lead to changes in ecosystem properties but can
also hamper reintroductions through predation.
Attempts to recover razorback suckers ( Xyrauchen
texanus ), an endangered piscivorous fi sh species, by
reintroducing them into their native range of the Colo-
rado River have not been successful because of preda-
tion on the young suckers by non-native fi shes
(Johnson et al . 1993 ).
In another study, Bergerud and Mercer (1989)
reviewed 33 reintroductions of caribou ( Rangifer
tarandus ) that took place in eastern North America
between 1924 and 1985. Twenty introductions
resulted in sustained populations and 13 failed, of
8.4
THE REINTRODUCTION SITE
Reintroduction in the core of the historic range of a
species has sometimes been indicated to be better than
reintroducing along the periphery (Griffi th et al . 1989 ;
Wolf et al . 1996). However, Lomolino and Channell
(1998) found that 23 out of 31 species of endangered
mammals persisted on the periphery, rather than in the
core or central portion of their historic range. In addi-
tion, persistence was greater for insular than for
continental populations. According to Lomolino and
Channell, the peripheral part of the range encom-
passes a much more diverse collection of habitats and
environmental conditions than the core sites, at the
centre of the species' range. They referred to the Cali-
fornia condor ( Gymnogyps californianus ) which was
also succesfully released to a site in northern Arizona,
well outside the condor's present range, but also pro-
viding protection from anthropogenic threats. From
their review of reintroductions of marsupials in Aus-
tralia, Short et al . (1992) came to the conclusion that
the success rate of island introductions (60%) was far
greater than for those in mainland Australia (11%),
even though the successful island introductions were
all to islands with no historic record of the occurrence
of the reintroduced species. Success of introduction of
these macropods appeared to depend critically on
control or exclusion of exotic terrestrial predators such
as foxes and cats.
A crucial aspect of any reintroduction plan is an
assessment of the availability and quality of the
reintroduction site. Reintroductions have a chance of
success only if the habitat and landscape requirements
of the species are satisfi ed over the long term. The area
should have suffi cient carrying capacity to sustain
growth of the reintroduced population and support a
viable self-sustaining population over time. Identifi ca-
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