Science may have figured out how an invasive plant spreads

With city growth and urban sprawl, could these changing landscapes be giving invasive species a competitive edge?

Scientists at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) say the answer may be yes, according to a new study from the UF/IFAS Invasion Science Institute. Their research suggests that some invasive plants are adapting to urban environments in ways that help them tolerate hotter, drier conditions, potentially preparing them to better withstand the impacts of a changing climate.

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The findings suggest that cities may serve as a training ground for invasive species. Many urban areas are hotter, drier and have more stressful conditions than surrounding rural landscapes, and invasive species may be adapting to those challenges. Those adaptations could then help them survive not only in cities but potentially spread into surrounding areas as climate change progresses.

"Urban-evolved invasive species may be well suited to future climate conditions, providing them an advantage over native species and complicating management efforts," said Luke Flory, director of the institute and associate chair of agronomy.

The researchers tested this idea using daisy fleabane, a plant native to North America that has become a widespread invader in Europe and parts of Asia. They collected seeds from populations growing in urban and rural areas around Zagreb, Croatia, and then grew the plants under simulated climate change conditions in specialized growth chambers at UF.

The researchers found an unexpected difference. Plants from urban populations were smaller than their rural counterparts under controlled conditions, suggesting more conservative growth, but were better able to withstand heat and drought.

When the plants were exposed to warmer temperatures, drought or both, the urban populations were less affected than the rural populations. The plants' ability to tolerate those conditions increased as the level of urbanization at the locations where the seeds were collected increased.

"We documented large differences in plant performance between rural and urban populations based on our experimental treatments that mimicked conservative predictions for warming and lack of rainfall for the area," said Drew Hiatt, the study's co-author and a doctoral student. "In reality, environmental stressors rarely behave so regularly, and it's likely that we would see even greater differences under a more prolonged drought or a more intense summer heat wave."

Cities serve as major entry points for invasive species because of travel, trade and the movement of people and materials. Researchers stress that the findings are important because cities are expanding around the world, while climate change is creating warmer and, in some places, drier conditions. An invasive species that adapts to the tough conditions of a city could potentially be better prepared to survive as those conditions spread beyond urban areas.

"Expanding urbanization and the rapid increase in global travel and trade mean that the importance of cities as hubs for the introduction and spread of invasive species will only increase." said Flory. "Improving understanding of the evolution of invasive species in urban areas is critical for predicting and mitigating the spread and impacts of invasive species under future climate conditions."

The researchers further said the findings could change how scientists and land managers think about invasive species in cities. Urban populations may not simply be sources of new invasions. They could also generate populations that are adapted to environmental stress that will become increasingly common in the future.

Researchers say more work is needed to determine how common this pattern is among invasive species and whether these adaptations consistently make urban-evolved invaders more successful.

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ABOUT UF/IFAS
The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state's agricultural and natural resources industries, and all Florida residents.

ifas.ufl.edu|@UF_IFAS

ABOUT ISI
The mission of the University of Florida Invasion Science Institute (UF/ISI) is to facilitate interdisciplinary research that advances our understanding of the causes and consequences of invasive species; generates innovative approaches to reduce invasions and their impacts on natural, agricultural, and urban systems; and train the next generation of invasion scientists. UF/ISI has over 190 affiliates and collaborators with a variety of backgrounds and expertise.

invasionscience.ufl.edu | @invasionscienceuf