Invasive species are a threat to biodiversity and ecosystem services worldwide. Humans have been transporting non-native species both intentionally and unintentionally ever since they first began exploring the globe; however, the rates of invasion, and thus the impacts of invaders, have greatly increased in recent decades in concert with increasing global commerce.
For centuries ecologists have been fascinated by the question of what allows a non-native species to be successful in a new place. I am seeking to understand the relative roles of plant traits and nutrient availability in predicting species invasion.
First, I am testing the hypothesis that species invade because they possess novel abilities, or traits, that allow them to utilize resources in ways that the natives cannot. This hypothesis is based on the concept that each species has a "niche," and that if two species are too similar, they will compete strongly for the same resources, resulting in one of the species being excluded from the community. Thus, in addition to investigating the role of plant traits, I am asking whether increasing resource availability allows non-native species to invade. Nitrogen is one of the most important limiting nutrients for plant growth, and is becoming increasingly available in natural areas as a consequence of pollution from tailpipe emissions and agricultural fertilizer runoff.
To ask these questions I am working with a group of researchers at Long Term Ecological Research sites across North America. Many sites have conducted nitrogen addition experiments, and documented which species increased or decreased in abundance, and whether new species invaded. I have assembled a database including the traits of the species in the experiments, and their responses to nitrogen addition. I expect that non-native species differ in their traits as compared to the native species at each site, but that nitrogen addition would allow invasion regardless of functional traits, due to decreased competition for this limiting resource.