Science tells us invasive species — like the spotted tilapia — are always on the move, making it difficult for scientists to simulate their spread and predict where they will go next.
Researchers at the University of Florida Institute of Food and Agricultural Sciences took a deep dive to understand why certain locations are more susceptible and attractive to invasions by non-native plants or animals, making them prime targets for these species to spread.
What they came up with is a novel approach updating what scientists call environmental resistance (ER) modeling that adds a layer researchers consider has been missing from the modeling strategies.
The study focused on the eastern United States, a hotspot for invasive species. Florida, for example, has more invasive vertebrates than any other state, while the Great Lakes region and the northeast are major battlegrounds for invasive plants, said Yunpeng Liu , a post-doctoral researcher affiliated with the UF/IFAS Invasion Science Research Institute and lead author of the research. By analyzing patterns of invasion in these areas, the researchers identified which kind of environmental resistance modeling play the biggest role in stopping or allowing the spread of invaders.
The findings, published in the Journal of Biogeography , offer a roadmap for identifying invasion-prone areas before new species get a foothold, which can serve as a fundamental tool for conservationists and land managers battling biological invasions.
"Traditionally, scientists have used climate-based models to predict where invasive species might spread," said Liu. "These models assume if a species thrives in one climate or condition, it will do well in a similar environment elsewhere.
Liu argues this approach has limitations because it lacks the ability to consider how quickly invasive species can adapt or how local ecosystems can resist new potential invaders.
"Most important, traditional modeling strategies do not predict invasion spread well if we do not know much about the suitable climates of the invasive species or we are not sure about their adaptation after they colonize into new habitats," he said. "What we came up with is an update to ER modeling that adds the necessary layer that has been missing.
ER modeling measures how difficult it is for invasive species to establish in a new area. The difficulty is determined by how similar of a location's existing variety of species to that of its neighboring invaded area.
The more similar the species gather in a place to the already invaded place, the more likely a place is to be invaded.
The authors improved the ER modeling strategy with a new approach. Besides considering species similarity, they also developed alternative ER models by measuring environmental resistance using other factors such as soil type and human activity. They simulated the observed invasive distributions with each ER model and identified the best model that most accurately simulated invasive distributions. Then the best model was used in predicting the invasion spread in the eastern United States.
"The ER model based on native species similarity was the best model for predicting current spread, not just for invasive plants but also a suite of invasive animals. This means that the key drivers on invasion spread in Florida are native species similarity, rather than other factors including climate, soil type or human activity," he said.
The study also explored how temperature shifts might alter invasion risks. As temperatures and ecosystems change, the movement of native species varieties also changes, resulting in some areas becoming more vulnerable to invasion, while others may develop stronger natural defenses.
"The findings suggest that native species groupings could become more similar in the future than what they are today, leading to an increase in the spread of most of the invasive species, especially for those who have already occupied a wide range of habitat," said Liu. "The regions near large cities, which were Florida's invasion hotspots, will be under high invasion risk in the future.
This research provides valuable insights for ecologists, land managers and policymakers working to combat the spread of invasive species, he said. Understanding the interplay between invasive species and their new environments could lead to more effective strategies for protecting native biodiversity and maintaining ecological balance.
