approximately 8% of terrestrial non-native species, 31% of non-native insects, and 28% of non¬ 
native fishes have had beneficial effects for humans and industry, such as species that provide 
biocontrol or serve as a foundation for agriculture (OTA, 1993). Further complicating the 
definitions of invasive species are those species that are considered damaging in one area but 
beneficial in another. The Asiatic clam (Corbicula fluminea ) is one such example; it invaded a 
tidal marsh in the Potomac River in the late 1970s and increased water clarity to a level at which 
submerged aquatic vegetation reappeared and various aquatic bird populations returned to the 
area (Phelps, 1994). In other regions this AIS clogs intake pipes, damages industrial water 
systems, and alters habitat. Only a small percentage of non-native species become invasive and 
cause severe ecological and/or economic damage (OTA, 1993). For those species that do 
become invasive, their impacts can be devastating. Invasive species can threaten the very 
existence of native species in the invaded environments (Clavero and Garcia-Berthou, 2005; 
Novacek and Cleland, 2001; Mack et al., 2000). Invasive species are a major cause of 
extinctions worldwide—48-62% of fish extinctions (68% of North American fish extinctions), 
50% of bird extinctions, and 48% of mammal extinctions (Clavero and Garcia-Berthou, 2005; 
Harrison and Stiassny, 1999; Miller et al., 1989). It should be noted that invasive species are 
generally not the only cause of these extinctions; invasive species are the sole cause for only 2 of 
the 40 extinct fish taxa in North America (Miller et al., 1989). In the U.S. alone, damage and 
losses from invasive species are estimated at approximately $120 billion annually (Pimentel et 
al., 2005). Also, despite advances in understanding what makes environments suitable for 
invasion and determining characteristics of species capable of invasion, it is still difficult to 
predict which species will become invasive (Richardson and Pysek, 2006; Kolar and Lodge, 
2001; Lonsdale 1999; Rejmanek and Richardson, 1996). 
In this report we focus on AIS, including coastal, freshwater, wetland, and riparian 
species that are already problematic in one or more states and have the potential to expand into 
neighboring states as climatic conditions change. Species can also become invasive when 
introduced into areas with similar climates as their host climate, such as species from the Ponto- 
Caspian regions to the Great Lakes. Thus, we rely on the definition from Executive Order 13112 
that the species has economic, ecological, or human health impacts to be considered invasive. 
However, because climate change has the potential to fundamentally change ecosystems, the way 
in which environmental managers differentiate and define native, non-native, and invasive 
species will also need to change in order to manage for changing threats. 
AIS can cause a wide range of ecological impacts, including loss of native biodiversity, 
altered habitats, changes in water chemistry, altered biogeochemical processes, hydrological 
modifications, and altered food webs (Dukes and Mooney, 2004; Ehrenfeld, 2003; Findlay et al., 
2003; Simon and Townsend, 2003; Eiswerth et al., 2000; Gordon, 1998). Wetlands, including 
1-5 
