examples are increasing (Parmesan, 2006). An example of an aquatic plant expanding into 
higher altitudes is the threadleaf water-crowfoot (Ranunculus trichophyllus ), which has invaded 
previously non-vegetated lakes in the Himalayas, an invasion attributed to climate change 
(Lacoul and Freedman, 2006). Tropical aquatic snails are another example of species whose 
ranges may expand under a changing climate. These snails are carriers of a specific genus of 
trematodes or blood flukes native to tropical and sub-tropical regions of the world that cause the 
disease schistosomiasis. These blood flukes could impact human health if these tropical aquatic 
snails, move northward as temperatures warm and conditions become more humid (Tol, 2002). 
While these aquatic species have not caused the types of damages attributed to mountain pine 
beetles, the potential exists for other AIS to cause further or unforeseen ecological or economic 
damages. 
1.5. CLIMATE CHANGE IMPACTS ON INVASIVE SPECIES 
Climate-change-induced alteration of ecosystem conditions can enable the spread of 
invasive species through both range expansion and creation of habitats and conditions suitable 
for newly introduced invasive species. Altered conditions such as increased atmospheric carbon 
dioxide, modified precipitation regimes, warming ocean and coastal currents, increased ambient 
temperature, and altered nitrogen distribution can increase invasive species success in some 
contexts (Ziska et al., 2007; Ziska, 2003a, b; McCarty, 2001; Dukes and Mooney, 1999). 
Research on climate change and invasive species is limited; however, many studies on potential 
climate-change impacts to aquatic systems and AIS exist, and several are highlighted here. 
A number of scientific studies have examined whether increased atmospheric carbon 
dioxide may enable invasions; however, because most attempts to predict invasions have been on 
a small scale and knowledge of invasions is limited, predicting the effects of increased carbon 
dioxide is uncertain. The effects of carbon dioxide enrichment in aquatic ecosystems, especially 
with respect to AIS, are still much less well understood than in terrestrial ecosystems, with the 
exception of recent research on ocean acidification and consequences for coral reef ecosystems 
(Cao et al., 2007; Pelejero et al., 2005; Scavia et al., 2002). Research indicates that increased 
carbon dioxide in ocean and freshwater environments may alter macro- and micro- algae and 
plant dynamics (Feely et al., 2004). For example, Chen et al. (1994) found that increased carbon 
dioxide may cause the invasive aquatic plant dioecious hydrilla (Hydrilla verticillata) to increase 
its growth rate at elevated temperatures (e.g., maximum effects of temperature on growth were 
recorded at 25°C). Thus, as temperatures and carbon dioxide levels rise, hydrilla has the 
potential to spread more rapidly within and outside of its current range. Weltzin et al. (2003) 
examined how elevated carbon dioxide levels affect plant invasions in various ecosystems and 
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