species diversity) affect its ability to resist nonindigenous species invasion (e.g., Hobbs, 1989; Case, 1990; Tilman, 1997; Stachowicz et al., 1999, 2002a). Often the most reliable predictor is the invasiveness of a species in situations with similar environmental characteristics (Forcella et al., 1986; Gordon and Thomas, 1997; Reichard and Hamilton, 1997).

Recent work has shown that relatively simple approaches may be used to address why some introduced species rapidly spread and flourish while others do not. Kolar and Lodge (2002) studied a number of nonindigenous fish species introduced into the Laurentian Great Lakes and found that different life history traits were important during different phases of the invasion process. Species that grew relatively quickly and had a wide range of temperature and salinity tolerances tended to be most successful during the establishment phase of the introduction. In contrast, species that rapidly spread only after becoming established typically had slower growth rates and a more limited range of temperature tolerance. Those species that eventually were categorized as “invasive” generally had wider salinity tolerances and were capable of surviving lower water temperatures than noninvasive species. These results demonstrate the importance of assessing stage-specific processes and patterns of successful and nonsuccessful invasions. Although the outcomes are habitat specific, the overall approach for predicting invasion success could be applicable to marine invaders. For example, a comparison of the survival patterns of different species as they are transported along a coastline provides useful information on the environmental tolerances of those species—information that is essential in studying the early phases of the invasion process.

Ecosystems that have reduced biodiversity or are under stress from environmental degradation and climate change appear to be more vulnerable to invasions. For example, Stachowicz et al. (2002b) demonstrated that enhanced species diversity directly increases the resistance of subtidal fouling assemblages to invasion and that surveys in a number of coastal habitats in southern New England also revealed an inverse correlation between resident species richness and the number of nonnative species in those habitats. Climate change has its greatest impact where invasive species occur at the southern and northern boundaries of ecosystems (see Root et al., 2003, for a recent meta-analysis). Temperate coastal regions appear to be particularly prone to invasion by nonnative species due to the effect of climate change on invasion by nonnative species. Stachowicz et al. (2002b) have correlated a doubling in the abundance of invasive ascidians in eastern Long Island Sound with a significant increase in seawater temperatures over the past two decades in that region. Sauriau (1991) correlated small increases in seawater temperatures with the spread of a gastropod, Cyclope neritea, initially introduced with shipments of the

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