Biology Reference
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Theoharides and Dukes 2007). Further, human action was included as a major
driver of the transportation of alien species (vector science) (Ruiz 2003; Mooney et
al. 2005; Kowarik and von der Lippe 2007). This enabled the integration of differ-
ent disciplines such as social sciences, economics, law, and natural sciences for the
study of biotic invasions. However, although vector science has helped us under-
stand and manage the spread of alien species, it did not solve the problem of under-
standing and managing impacts in invaded habitats.
Our typology (Table 5.1) attempts to frame invasion issues based on habitat
states and their human valuation. There are several lines of previous research that
point in a similar direction. Research has attempted to generalize knowledge about
the vulnerability of habitats to invasions, based on general ecological processes
such as disturbance regimes, resource availabilities, or species diversity (Lonsdale
1999; Levine et al. 2004; Fridley et al. 2007), but interactions between species traits
and habitat characterization have not been at the central focus. It has long been
argued that the spread and impact of invasive species in a habitat has to be under-
stood and generalized as a species-by-environment interaction (Richardson 1990;
Morse 2004; Callaway 2006). A multitude of studies have shown the relevance of
anthropogenic habitat modification and land use for explaining biotic invasions
(Hobbs 2000; Maskell et al. 2006). However, such research on the interactions
between species traits and habitat characteristics and/or land use has so far mainly
compiled case examples. Interestingly, social geographers have also worked on a
theoretical understanding of land use changes and biotic invasions (Robbins 2001;
Schneider and Geoghegan 2006). Robbins (2001) for instance discussed abandoned
land and proposed the term “quasiforests” to account for such hybrid landscapes
that fall in-between the natural and the social. Our framework is derived from the
realities that managers are confronted with and emphasizes the context-dependence
of invader impacts. We suggest our typology may be a good starting point to bring
together theoretical thinking from the natural and social sciences and improve our
conceptual and practical understanding of impacts of invasive species.
Acknowledgments
We thank Jake Alexander, Paul Krushelnycky, and two anonymous reviewers
for very helpful comments on earlier versions of the article, and Eva Schumacher for assistance
with the preparation of the figures. CK was supported by USDA NRI Cooperative Research,
Education, and Extension Service Grant # 2006-35320-17360.
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