Biology Reference
In-Depth Information
projects will be well adapted to local conditions, will interact with native mutual-
ists, and may be selected to have a strong influence on ecosystem properties.
The choice between native and alien species for designed habitat has a prag-
matic and a more fundamental dimension. From a pragmatic perspective, we may
ask if and when alien species are more effective as tools for a particular purpose
in an ecological design project than native species. Arguments for alien species
may be that there is a larger pool of species available (especially species with
novel traits such as nitrogen-fixation that may not be present in the native flora),
their ecology is better known, and alien species may perform better because they
are less attacked by pests or herbivores (i.e. enemy release). Arguments against the
use of alien species may be that the chances are higher that they have negative
side-effects (e.g., form mono-dominant stands and are difficult to control) and
lower that they have nontarget positive side-effects (e.g., provide food and habitat
to a wide variety of native species). On a more fundamental level, it is uncertain if
and when alien species may be valued positively as long-term constituents of the
designed habitats (Donlan et al. 2005; Nicholls 2006; McLachlan et al. 2007). The
idea to introduce alien species as ecological analogs of extinct species has gained
momentum (Donlan et al. 2005; Nicholls 2006). In Mauritius for instance, the
translocation of Aldabran giant tortoises as ecological analogs for the extinct
Mauritian giant tortoises is currently being investigated (cf. Zavaleta et al. 2001;
Nicholls 2006). Another consideration in the context of designed habitat may be
promotion of species that are threatened in their native range because of global
change dynamics such as climate change. Such species may be translocated into
designed habitat (assisted migration, McLachlan et al. 2007). More generally, in
an era of global change, introduction of alien species for ecological design may
become increasingly relevant. It may, for instance, be necessary to introduce alien
species to a habitat to increase its resilience to climate change, or assist the migra-
tion of whole habitats.
5.6.4 ResearchFocus
Invasions into designed habitat have received little scientific study. Many basic
ecological questions related to diversity-ecosystem functioning, seed limitation, or
the importance of soil microbe communities are of high relevance to ecosystem
design (Young et al. 2005). In fact, their intermediate complexity between artificial
model systems, such as microcosms, and natural ecosystems provides a convenient
compromise between tractability and real-world applicability for ecological
research. If a designed habitat is isolated, e.g., on a small island, deliberate intro-
duction of alien species may be a convenient system for real-world risk screening
prior to the species' broader introduction in a region. Because alien species that
have a high potential to assist rehabilitation of degraded sites also have a high
potential to become disruptive (Richardson et al. 2004), research is needed to iden-
tify effective strategies for reducing these risks. The safest option may be to breed
