By Aliya Uteuova
For years, scientists have attempted to unravel why some invasive plants escape the grazing of hungry herbivores.
It turns out, the chemical makeup of some invasive plants protects them from being eaten. In a recent paper, scientists have taken a closer look at invasive plant species in forests of the Smithsonian Environmental Research Center (SERC) in Edgewater, Md. The study, published in the August issue of Ecology and Evolution, found that five common plant invaders have a chemistry quirky enough to make animals like deer and insects avoid them. The results suggest that their strange chemistry has helped fuel some successful invasions into Mid-Atlantic forests.
“Human activity has dramatically reshaped the planet,” said Brian Sedio, lead author of the paper and an assistant professor at The University of Texas at Austin. Redistributing invasive species means that we often have the same rats, same pests, same weeds around the world, which comes with a huge economic impact.
The research site contains relatively young forests, with trees 75 to 120 years old, and species typical of those in the mid-Atlantic United States. Native species include American beech, oak, tulip poplar, sweet gum and green ash. The introduced invasives include vines, woody shrubs, wineberries, Japanese honeysuckle and grasses like Japanese barberry and Japanese stiltgrass.
Overall, the invasive plants were chemically different from the natives. But five invaders particularly stood out, all invasive plants also commonly found in Delaware. The tree of heaven (Ailanthus altissima), the princess tree (Paulownia tomentosa), Japanese barberry (Berberis thunbergii) and Japanese stiltgrass (Microstegium vimineum) largely escaped deer and insects alike. The fifth, an invasive vine called Asian bittersweet (Celastrus orbiculatus), didn’t deter hungry deer but did turn off insects.
For the hungry animals in the study, the scientists focused on the diets of Japanese beetles, woolly bear caterpillars and white-tailed deer, the predominant large herbivore in the region. These animals stayed clear of the invasive species that had the most exotic chemistry.
“Think of people who refuse to eat spicy or exotic food,” said John Parker, one of the co-authors of the paper and principal investigator of SERC’s Terrestrial Ecology Lab. “Native herbivores might not eat invasive plants because they have chemistry that they’re not used to eating.”
Parker collected 231 leaf samples. Scientists were able to identify the compounds in the leaves by blasting them into pieces, matching them against a library of known compounds and comparing fragmentation patterns.
“Before this new technology, we didn’t have the chemical know-how to isolate and identify so many chemicals in so many species all at once,” Parker said.
The fact that some invasive plants are less tasty to herbivores is contributing to their successful, widespread invasion in regional forests. For Sedio, figuring out the white-tailed deer’s response is the next step to understanding why herbivores generally don’t prefer invasive species.
“Understanding mechanisms behind biological invasions can help us prevent them in the future and address the problem of invasive species,” Sedio said.
The study, “Chemical novelty facilitates herbivore resistance and biological invasions in some introduced plant species,” is available at onlinelibrary.wiley.com/doi/full/10.1002/ece3.6575.
Aliya Uteuova worked as the summer and fall science writing intern at the Smithsonian Environmental Research Center on the Chesapeake Bay in Edgewater, Md. Learn more about the research center at https://serc.si.edu/
