concluded that increasing carbon dioxide levels will cause increases in resources, plant 
production, soil moisture, and nitrogen uptake, all of which create favorable invasion conditions. 
Increased temperatures and altered precipitation regimes are likely to have larger effects 
on AIS than increasing levels of carbon dioxide. One study of emergent macrophytes in lakes 
showed that increased temperatures led to larger increases in biomass than increased carbon 
dioxide levels (Ojala et al., 2002). As in terrestrial environments, responses to carbon dioxide 
may be species specific, but other environmental variables like water temperature and 
hydrological regimes may be more important drivers in changing the establishment, spread, and 
impact of AIS. 
Climate change is predicted to alter precipitation patterns, leading to droughts in some 
areas and flooding in others due to increased storm intensity. Knowledge of the effects of 
climate variability, which also causes droughts and floods, can offer some insights into how 
ecosystems respond to the stress of altered hydrology (Shafroth et al., 2002). There is much 
evidence in the invasive-species literature that ecosystem disturbances encourage pioneer 
species, and many invasive species are pioneers (Byers, 2002; Schnitzler and Muller, 1998). 
Thus, changes in precipitation due to climate change may affect AIS establishment and dispersal. 
Increased rainfall may allow for greater dispersal of upstream invasive species to downstream 
habitats. Zedler and Kercher (2004) hypothesize that wetlands are highly vulnerable to invasions 
because wetland invasive plant seeds are frequently dispersed by water. Lonsdale (1993) finds 
that flooding and rainfall are important factors affecting dispersal of the invasive weed Mimosa 
pigra in Australia. The size of the area colonized related to the amount of rainfall in the previous 
wet season, and the data suggest that seed dispersal by flotation is key to rapid wetlands 
expansion. 
Increasing ocean temperatures also may enable new species invasions. Stachowicz et al. 
(2002) compare recorded sessile invertebrate species recruitment and establishment with 
temperature data. Their research shows that introduced ascidians (sea squirts) recruit earlier in 
years with warmer winter water temperatures while the recruitment of native ascidians did not 
significantly change with variation in winter water temperature. Because community 
composition is often determined by which species settles first, introduced ascidians may out- 
compete native ascidians as ocean temperatures warm. The authors also show that introduced 
ascidians have higher growth rates than native species at high temperatures. The authors 
conclude that rising mean winter water temperature is a stressor that may lead to increased 
invasions by non-native species in New England. In addition, as coastal currents warm, species 
may shift their ranges northward and become invasive in new areas. Barry et al. (1995) 
examined data on intertidal invertebrate assemblages in California using records that span over 
60 years. These data show that near shore water temperatures increased by 0.75°C and summer 
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