The number of invasive species is growing every year, as plants, animals, and microbes are introduced into habitats where they did not historically occur. Invasive species are of concern for scientists and land managers because of their detrimental effects on biodiversity and ecosystem functioning. To help mitigate their effects it is important to understand what processes cause a small fraction of introduced species to become troublesome invaders.
I am interested in learning if and when natural enemies influence invasive species performance, and how the fitness effects of natural enemies change over the course of invasion. To address my questions I use a combination of observational field studies, common gardens and meta-analyses of existing work. Located in old-field communities near the Kellogg Biological Station, my experiments look at the effects of biotic interactions on species of three statuses – native, exotic non-invasive, and invasive.
Natural enemies, such as herbivores and pathogens, are major drivers of both plant community structure and population dynamics. As a result, enemies play key roles in influencing plant distributions, including spread of exotic species that escape enemies during biological invasions. Elton (1958) was the first to recognize the dual role played by natural enemies during invasion: release from enemies from the native range may play a role in the explosive population growth rates of invasive species, and acquisition of enemies in the exotic range may explain why so many of the plants introduced around the world fail to establish and spread. My field research addresses these predictions, and I ask:
- Do invasive, exotic, and native species experience different amounts of damage from natural enemies?
- Does enemy release result in increased performance for invasive species compared to native and non-invasive exotic species?
- Do the benefits of enemy release diminish over time as invasives integrate into natural communities?
Are altered biotic interactions during invasion a general mechanism to explain invasive success?
While many studies have shown differences in enemy damage between native, exotic, and invasive species it is not yet known if these differences translate into fitness effects. Though a plant may experience less damage in its exotic range, or compared to native species in its exotic range, this does not necessarily translate into increased performance and the potential to invade if damage has minimal effects on plant fitness. To fully examine the role of biotic interactions during invasion, we must determine if and how often enemies affect the fitness of introduced and native species.
To address this question I am currently performing a meta-analysis of the invasion literature, looking at studies that have manipulated biotic interactions on native, exotic, and invasive species.
Allelopathic effects of Alliaria petiolata on rhizobia and its implications for native legume performance
Invasive species Alliaria petiolata (garlic mustard), has been shown to harm a common soil mutualists for native plants, mycorrhizal fungi. Its allelopathy reduces the performance of this key mutualist, thus indirectly decreasing the performance of their plant mutualist partners. It is possible that these allelopathic effects may extend to other soil biota. Along with Tomomi Suwa and two undergraduate collaborators (Cristy and Tina), we are testing if A. petiolata’s allelochemicals have similar negative effects on another important symbiotic organism: rhizobia, a nitrogen fixing bacteria that forms symbiotic relationships with legumes.