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or genetically engineer sterile varieties of these species (Ewel et al. 1999). Designed
habitat may be foremost an opportunity for experimentally addressing the natural/
artificial dichotomy from both a natural and social sciences perspective. How do
alien and native species differ in their effects on biotic communities and ecosys-
tems? Will these differences between native and alien species change with global
change and native species loss, and how does this affect how we define and value
“high quality nature”?
5.7 Discussion
Our typology for understanding, valuing, and managing invasive species impacts is
based on different habitat types (anthropogenic, reference, abandoned, and
designed). The four habitat types represent prototypes, but in reality the differences
between them are sometimes blurred and may become more so in the future. For
instance, land may be managed simultaneously for biodiversity and other products
or services, and these habitats are hybrids of anthropogenic and designed habitat.
In some places, abandoned land may transform into reference habitat over time, but
the exact transition point is not clearly defined. In some cases, additional refine-
ment of categorizations could help to clarify biotic invasion issues. For instance, in
anthropogenic habitat, urban areas, intensive agriculture and extensive or tradi-
tional agriculture differ as contexts for biotic invasions. Nevertheless, we think that
our typology represents a valuable first sketch, demonstrating how a habitat-based
framework could advance invasive species research and management.
5.7.1
Toward a Habitat-Based Framework for Invasive
Species Research
Initially, invasive species research has attempted to separately generalize traits of
problematic invaders (invasiveness) and characteristics of vulnerable habitats (inva-
sibility) (Drake et al. 1989; Williamson 1996; Lonsdale 1999; Kolar and Lodge
2001). However, although this approach helped to identify heuristics to predict the
invasiveness of species and the invasibility of habitats, it did not provide an integra-
tive framework to understand the interactions of species, environment, and human
action or the dynamics of invasions in space and time (Kueffer and Hirsch Hadorn,
2008). Phase-transition models were a first successful attempt to gain a more inte-
grative understanding of biotic invasions (Richardson et al. 2000; Kolar and Lodge
2001; Dietz and Edwards 2006; Facon et al. 2006; Richardson and Pysek 2006;
Theoharides and Dukes 2007). In these models, an invasion is characterized as a
sequence of distinct phases. These phases typically include introduction, establish-
ment, and spread in a new area. Phase-transition models have allowed specifying
relevant ecological processes for different phases (Dietz and Edwards 2006;
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