It is often recognized that invasive species proliferate in disturbed environments. Several mechanisms have been suggested to explain this pattern, including enhanced propagule supply (Lonsdale 1999, Brown and Peet 2003, Von Holle and Simberloff 2005), selection regime modification (Byers 2002), and relaxation of competition in such non-equilibrium environments (Davis et al. 2000, Stachowicz and Byrnes 2006). The interaction of disturbance and predator influence may be a particularly important, and heretofore unexamined, factor either mitigating or accentuating the influence of disturbance on invasion rates. Almost all models and theory to date deal with invasions on a single trophic level by examining how competition and the completeness of resource use influence invasion rates (e.g. Stachowicz et al 2002, Byers and Noonburg 2003). Our study also incorporates the importance of this competitive mechanism, but takes a fundamental step toward broadening invasion biology to embrace the role of other trophic levels, and thus moves invasion biology toward a more community-based, holistic perspective. 

Pollution directly alters communities by screening out or differentially killing certain species and life stages. Thus, communities that develop in polluted environments tend to have a lower diversity of species and under-utilized resources (Crowe et al. 2004).  Pollution also affects the operation of processes such as predation that normally cause large responses in the community (Kiffney 1996; Hamers and Krogh 1997). Depending on the relative susceptibility of predator and prey to contaminant exposure, pollution may effectively depress or elevate predation pressure. In marine fouling communities, pollution and predation both act to free up the valuable limiting resource of space (e.g., Nydam and Stachowicz 2007). But many invertebrate predators (e.g. flatworms, nudibranchs and whelks) are likely to be more susceptible to contaminant exposure than their sessile prey (barnacles, oysters and polychaetes). Hence pollution may generally act to depress predation levels in these systems (Lee and Johnston 2007). Because in many space limited systems the amount of space occupied correlates directly with the invasibility of the community, we propose that the direct influences of pollution as well as its indirect influence, via predation, will have strong interactive effects on community invasibility.  Therefore, we propose a comprehensive study to examine the relative influence of these direct and indirect effects of pollution on susceptibility of native communities to invasion.