• “Industrial, agricultural, and other human activities, coupled with an expanding world 
population, are contributing to processes of global change that may significantly alter the 
Earth habitat within a few human generations,” and 
• “Such human-induced changes, in conjunction with natural fluctuations, may lead to 
significant global warming and thus alter world climate patterns and increase global sea 
levels. Over the next century, these consequences could adversely affect world 
agricultural and marine production, coastal habitability, biological diversity, human 
health, and global economic and social well-being” (GCRA, §101 [a]). 
The U.S. EPA is one of several U.S. agencies and organizations that is conducting global 
change research. The U.S. EPA’s Global Change Research Program (GCRP) in the Office of 
Research and Development is assessing the effects of global change on aquatic ecosystems and 
their services in the context of other stressors and human dimensions in order to improve 
society’s ability to respond and adapt to the future consequences of global change. The GCRP 
emphasizes the role of climate change, climate variability, and land-use change as global change 
stressors. Increasingly, scientists and policy-makers have recognized invasive species as global 
stressors because of their significant effect on ecosystems (Mooney and Hobbs, 2000; Vitousek 
et al., 1997a). 
1.3. INVASIVE SPECIES AND ECOSYSTEM IMPACTS 
The movement of species into new areas is a natural phenomenon that has occurred 
throughout evolutionary history (Tinner and Lotter, 2001; Graham et al., 1996). In modem times 
the movement of species has been augmented by humans operating in a globalized world. In the 
Great Lakes, for example, intense vessel traffic from international trade is the major vector for 
introduction of non-native aquatic species. This region has the highest known introduction rate 
for freshwater ecosystems, with one new non-native species being discovered every 28 weeks 
(Ricciardi, 2006). San Francisco Bay has the highest overall introduction rate as recorded from 
1961 to 1995, with one new non-native species introduced every 14 weeks (Cohen and Carlton, 
1998). The actual number of non-native species introduced into the U.S. is unknown. Estimates 
range from 6,600 since European settlement of the U.S. (Cox, 1999) to 50,000 species (Pimentel 
et al., 2005). 
Non-native species (also described as alien, exotic, or nonindigenous species) that are 
intentionally or unintentionally released into new environments can become invasive species. 
Executive Order 13112 (February 1999), which established the National Invasive Species 
Council, defines an invasive species as a non-native species the introduction of which causes or 
will likely cause harm to the economy, environment, or human health. In addition to this 
Executive Order, various federal laws relate specifically or are applicable to invasive species (see 
1-3 
