Understanding the factors that determine invasion success for non-native plants is crucial for maintaining biodiversity and ecosystem functioning. One hypothesized mechanism by which exotic plants can become invasive is through the disruption of key plant-mycorrhizal mutualisms, yet few studies have investigated how these disruptions can lead to invader success. We present an individual-based model to examine how several factors affect the dynamics of interactions between an invasive plant, Alliaria petiolata (garlic mustard)—a known disrupter of plant-mycorrhizal mutualisms—and the composition of the invaded plant community (i.e. subsequent changes in native-plant abundances). Three questions were investigated: (1) How does the strength of the mutualism between native plants and mycorrhizal fungi affect the resistance of the plant community to invasion by garlic mustard? (2) What is the threshold density that garlic mustard must reach to weaken existing plant-mycorrhizal mutualisms enough to establish itself in the community? (3) How do three natural history traits of garlic mustard (reproductive rate, dispersal ability, and allelopathic effects on mycorrhizal fungi) interact to influence the probability of invasion success?
Our findings indicate that high (i.e. obligate) and low (i.e. weak) mutualism strengths between native plants and mycorrhizal fungi were more likely to lead to dominance of garlic mustard, whereas intermediate levels resulted in greater resistance to plant invasion. Initial density of garlic mustard was also an important factor in determining invasion success, as initial densities ≥10% of the total plant population often led to invader dominance. Furthermore, we show that for garlic mustard, reproductive output and allelopathic effects were the best predictors for its successful establishment. Higher rates of reproduction and greater allelopathic distances frequently resulted in monocultures of garlic mustard. Overall, these findings suggest that land managers should not only prioritize the removal of invasive plants with high reproductive rates, but they should also incorporate restoration methods to help restore the mutualistic interactions between native plants and mycorrhizal fungi.