Biological invasions result when plants, animals, and other species are introduced into regions where they did not historically occur. Invasive species cause over $137 billion in damages to native ecosystems and human interests around the world every year. Yet, despite their importance and over 50 years of intensive study, there is no consensus about what underlies their success. The goal of this project is to test one of the key hypotheses explaining the success of invasive species: biological invasions occur because invasive plant species are not strongly impacted by competitors, predators, and herbivores in areas outside their native range. Additionally, while newly introduced species may receive little damage from novel enemies, this phenomenon may be temporary -- invasive species may acquire more enemies over time. These ideas will be tested by planting native, non-invasive introduced, and invasive introduced plant species into field environments where the presence of enemies (herbivores and disease) has been experimentally manipulated. A key prediction is that removal of enemies will not benefit invasive species, compared to native and non-invasive introduced plants, as they are already experiencing little damage from enemies. Further, invasive species introduced longer ago may start to resemble native species and benefit from the removal of enemies.
Given the economic costs and environmental harm caused by biological invasions, it is important to understand what causes them to differ from native and non-invasive introduced species. This research will help determine what factors contribute to invasion success; doing so can help predict and prevent future invasions. This work also will help to predict the long-term consequences of invasions (e.g., whether they will continue to be problematic or whether the accumulation of enemies will eventually limit their impacts). Results will be shared broadly, including academic audiences, the general public, and K-12 students. Working with elementary, middle, and high school teachers in rural schools across southwest Michigan, the co-PI will develop lesson plans and workshops for student and teacher development, covering topics such as invasion biology, community ecology, and evolution. The co-PI will continue to mentor undergraduate and high school students pursuing scientific careers.
Biological invasions result when plants, animals, and other species are introduced into regions where they did not historically occur. Invasive species cause billions of dollars in damages to native ecosystems and human interests around the world every year. However, despite their importance and over 50 years of intensive research, there is no consensus about what drives the success of invasive species. Schultheis is interested in understanding the mechanisms that explain the success of invasive species. Are there features that are shared by invasive species that differentiate them from native and non-invasive exotic species? Her research investigates the Enemy Release Hypothesis (ERH), one of the key hypotheses explaining the success of invasive species. The ERH states that biological invasions occur because invasive species are not strongly impacted by enemies, such as herbivores and disease, in their introduced ranges. She predicts that compared to native and non-invasive exotic plants, invasive species will receive less damage from enemies and be less impacted by this damage. Additionally, while newly introduced species may escape enemies, this benefit may be temporary and lost as introduced species acquire enemies from their introduced range over time. Schultheis tested these hypotheses using two approaches. First, she by planted native, non-invasive exotic, and invasive plant species into field environments where she manipulated the presence of enemies (insect herbivores, mammalian browsers, and disease). She found that, contrary to her predictions, invasive species received more damage from enemies than did native or non-invasive exotic species. Invasive species were equally impacted by this damage, meaning that enemies exert similar control over all three species types. Supporting her second hypothesis, she found that with increasing residence time and spread in the introduced range, invasive and non-invasive exotic species were more damaged and impacted by enemies. Her second approach was to conduct a meta-analysis, or synthesis of the existing literature addressing the ERH. By pulling together data on all studies that had grown native, non-invasive exotic, and invasive species with and without enemies present, she could see if her field experiment results fit a more general trend, while also extending into studies looking at invasive animals and other biotic interactions, such as competition, mutualisms, parasites, and interactions with the soil microbial community. The findings from the field experiment and meta-analysis both do not support the ERH and find that release from enemy pressures is not a general mechanism explaining invasive species success. Given the economic costs and environmental harm caused by biological invasions, it is important to understand what causes them to differ from native and non-invasive introduced species. Research by Schultheis can help determine what factors contribute to invasion success and can, therefore, help predict and prevent future invasions. Her work also will help to predict the long-term consequences of invasions (e.g., whether they will continue to be problematic or whether the accumulation of enemies will eventually limit their impacts). Schultheis has shared the results of her research broadly, including academic audiences, the broader community, and in K-16 classrooms. Working with elementary, middle, and high school teachers in rural schools across southwest Michigan, she developd lesson plans and workshops for student and teacher development covering topics such as invasion biology, community ecology, and evolution. She is proud to be one of the creators of Data Nuggets (http://datanuggets.org), activities that bring data from real scientific experiments into K-16 classrooms and guide students thorough the process of science.
