Environmental Engineering Reference
In-Depth Information
8.1 REINTRODUCTION OF SPECIES
AND RESTORATION ECOLOGY
ated movement of wild individuals or populations from
one part of their range to another.
Community, ecosystem and landscape changes and
transformations carried out in the past may have
major consequences for the success of reintroduction
attempts because the ecosystem or habitat at issue may
have become permanently unsuitable for the species of
concern, for example due to climate change (see
below, section 8.8). However, even when habitat suit-
ability is ensured, many reintroductions fail. There are,
indeed, many other factors involved in reintroduction
becoming either a success or a failure. Keystone
species , for example, play a critical role in communi-
ties, and their effects are generally much larger than
would be predicted from their relative abundance (see
also Chapter 2). If keystone species become threatened
or go extinct in their habitat it can be expected that the
system changes dramatically and that, next to trying
to reintroduce the keystone species into its habitat, the
changes may have become so extensive that reintro-
duction becomes very diffi cult. It has been shown
through modelling work that even random removal of
species can lead to cascading extinctions far beyond the
target one (Borvall et al . 2000 ; Lundberg et al . 2000 ),
and that cascading extinctions are positively related to
species abundance and connectivity (Law 1999 ). If
ordinary (i.e. nonkeystone) species can have such
effects, what can we expect if keystone species become
extinct? No clear fi eld data are available at present, but
this question stresses the need for the conservation of
keystone species while they are still present in their
original habitat.
In this chapter, I will highlight some of the impor-
tant aspects of the art and science of reintroducing
plant and animal species that largely determine the
outcome - either success or failure.
The very fi rst attribute of restored ecosystems mentioned
in the SER Primer on Ecological Restoration (SER 2004 )
is that 'the restored ecosystem contains a characteris-
tic assemblage of the species that occur in the reference
ecosystem and that provide appropriate community
structure'. In this context, intended introductions of
species are an important tool, because dispersal is very
often a major constraint, especially in highly frag-
mented habitats and landscapes. Thus, even if the SER
Primer speaks in terms of whole ecosystems for the
most part, restoring species diversity ( sensu Falk et al .
1996) is a crucial part of ecological restoration. More
specifi cally, this phrase refers to the reintroduction of
species or subspecies that have been lost or whose pop-
ulations have been seriously reduced and weakened for
various reasons.
In response to the increasing occurrence of reintro-
duction projects worldwide and to help ensure that
they achieve their intended conservation benefi t, the
Reintroduction Specialist Group of the International
Union for the Conservation of Nature (IUCN) Species
Survival Commission has developed guidelines (IUCN
1998) in the context of the IUCN's broader policies
pertaining to biodiversity conservation and sustaina-
ble management of natural resources. According to
the IUCN, the principal aim of any reintroduction
should be to establish a viable, free-ranging population
in the wild, of a species, subspecies or race, where it
has become globally or locally extinct, or extirpated.
The population should be reintroduced within the
species' former natural habitat and range, where it
should ideally persist with minimal or no need for
long-term management. The objectives of a reintro-
duction may include the enhancement of the long-
term survival of a species, the re-establishment of a
keystone species in an ecosystem (or an emblematic
species from a cultural point of view), or the mainte-
nance and/or repair of biodiversity in (semi)natural
landscapes. In the literature, both the terms reintro-
duction and translocation are being used. Strictly
speaking, these terms do not mean exactly the same
thing. Reintroduction is to establish a species within its
historical range through the release of wild or captive-
bred individuals following exterpation in the wild
(IUCN 1998). Re-establishment is often used as a
synonym, but implies that the reintroduction has been
successful. A translocation is a deliberate and medi-
8.2
SOURCE POPULATIONS
Individuals targeted for reintroduction can come from
various sources, and as a fi rst step a careful assessment
should always be made of the taxonomic status of the
candidate sources or provenances . Even though the
species concept as a basic taxon unit is controversial,
individuals should ideally be of the same subspecies as
those that were locally extirpated. Genetic studies
should be carried out, if possible, to determine the rela-
tive degree of taxonomic and genetic similarity between
possible substitutes and the pre-existing population.
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