Numerous experimental case studies have demonstrated competitive superiority of some non-native species over native species via a variety of mechanisms, including enemy escape, novel weapons, and inherent growth rate advantages (i.e. evolution of increased competitive ability, EICA). Nevertheless, few studies have attempted to relate competitive superiority of invaders to invasion success or community-wide impact. Furthermore, the relative importance of different mechanisms of invader competitive superiority (ICS) to invasion success and impact in relation to variation in disturbance regimes and characteristics of the resident community (e.g., species diversity) is not well understood. I used Lotka-Volterra competition models to simulate invasion of established resident communities and to test the relative predicted importance of different mechanisms of ICS (e.g., reduced density-dependent mortality, increased per capita competitive effect, increased growth rate) on resident communities. In addition, I examined how the different ICS mechanisms interacted with factors that potentially influenced resistance to invasion (i.e., disturbance severity and resident species diversity) to influence invasion success and impact. I examined the effects of varying niche overlap among resident species, but assumed complete niche overlap between resident species and the invader (commensurate with a hypothesis of niche partitioning among residents but not between residents and the invader).
Results/Conclusions In the absence of severe disturbances, all else equal, reduced density-dependent mortality in the invader (e.g., as predicted by enemy escape or more efficient resource use) resulted in the greatest invasion success and impact on the resident community. In contrast, invader advantages such as higher per capita competitive effects (e.g., novel weapons) and inherently higher growth rates (e.g., EICA) were less effective at promoting invasion success or impact except when following severe disturbances, suggesting that invaders with these types of competitive advantages over native species have difficulty increasing when rare within an undisturbed community with multiple species. Within undisturbed communities, increasing the numbers of resident species with low niche overlap was effective at decreasing invasion success. However, monocultures of a resident species equal in competitive ability to the invader were more effective than multi-species assemblages of competitively inferior resident species in resisting invasion. Results predict that the effects of different mechanisms of competitive superiority on invasion success and impact could depend on disturbances, native species diversity, and the competitive ability of the dominant native species in a community.