intentional stocking. Carlton (2000) identifies a slightly different set of global change and 
anthropogenic stressors affecting invasions in the oceans: overfishing, chemical pollution and 
eutrophication, habitat destruction and fragmentation, biological invasions (facilitating other 
invasions), and climate change. In the Great Lakes, human activities linked to aquatic invasions 
include clear-cutting and farming practices that increase sedimentation and water turbidity, 
industrial pollution, urbanization, and overfishing (Glassner-Shwayder, 2000). These examples 
show that there are many stressors interacting to facilitate the establishment and spread of 
invasive species and to influence the magnitude of their impact. Climate change will interact 
with existing stressors and may ameliorate or exacerbate their effects; however, little is known 
about the change in magnitude of effects due to climate change. 
Although the above examples illustrate that there are many stressors interacting with 
invasive species and climate change, land-use and land-cover changes remain the major global 
stressors that affect these other stressors (Vitousek, 1994). Land-use change and the ecosystem 
disturbances it causes can lead to more invasions (Hansen and Clevenger, 2005; Mack et al., 
2000). Nutrient loading due to increased agriculture, intensification of agriculture, or urban 
runoff can facilitate invasions of aquatic invasive plants (Lake and Leishman, 2004). Increased 
development can lead to degradation of habitats, and some studies demonstrate that degraded 
habitats are more prone to invasion than healthy environments (Mack et al., 2000). Hobbs 
(2000) discusses the complex nature of land-use changes and their effects on invasive species 
and habitat invasibility. Land-use changes include increased urbanization, deforestation, 
ecosystem fragmentation, and altered agricultural practices (intensification and abandonment). 
Two additional major changes in recent history that can alter ecosystem dynamics are 
increasing levels of human transformation and domination of ecosystems (Vitousek et al., 1997b) 
and increasing transport of species leading to a breakdown of biogeographical barriers (Cohen 
and Carlton, 1998). Hobbs (2000) describes the complex interrelationship between land-use 
disturbances and invasions further. For example, land transformation (e.g., increased nutrient or 
pollution runoff from conversion to agriculture or urban development) can enhance invasion by 
providing opportunities for establishment. Invasion, in turn, can drive land transformation (e.g., 
an invasive tree species can convert grassland into forest). These processes may feed back upon 
each other to facilitate further alteration, possibly causing an “invasional meltdown,” which leads 
to an acceleration in the number of invasive species and impacts (Ricciardi, 2001; Simberloff 
and Von Holle, 1999). 
Climate change will present a major stressor with which managers and decision-makers 
will need to be concerned, particularly in the context of interacting with other contributors to 
species invasions. However, scientific understanding of the complexity of invasions resulting 
from climate change, and making predictions that incorporate this understanding, is not yet well 
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