Invasive ants can threaten ecosystems by damaging plants at the root

Invasive ant species can be found in nearly every ecosystem on the planet, but the impact these invaders can have on plant health has only recently been studied by scientists. A new study published in Journal of Ecology is the first of its kind to discover that invasive ants can disrupt plant growth and photosynthesis by nesting at their roots, potentially threatening plants in tropical and subtropical regions around the world.

The research is led by biologist Pat Milligan, who has completed his doctorate. at UF in 2020 and is now an NSF Postdoctoral Fellow at the Pringle Lab at the University of Nevada, Reno. Todd Palmer, a biology professor at UF and a Ph.D. from Milligan. advisor, also contributed to the study.

While studying on site at a research center in Kenya, Milligan noted that some areas of the reserve had become heavily occupied by the invasive species Pheidole megacephala, known as “fat-headed ants”. The species had killed nearly all other native ants and many other native insects in the area. Milligan also began to wonder about the impacts of ants on plant health in the area.

In an article published earlier this year by Ecology Letters, Milligan et al. concluded that ants allow large herbivores like elephants to damage acacia trees, key players in ecosystem health. “Still, we had this kind of lingering question about how these invasive ants might directly interact with trees,” he said.

While roaming the center grounds, Milligan observed a peculiar pattern. He saw the invading ants forming networks of tunnels around tree roots, apparently attracted to the structure already in place to build their homes around. For two years, Milligan and his collaborators monitored ant-plant interactions through a series of greenhouse and field experiments.

The researchers found that plants with ant nests around their roots had higher baseline water stress. “They’re in that state of life that’s closer to drying out because of the loss of integrity of their root structure,” he said. The experiments also suggest that invasive ants cut a tree’s photosynthesis by more than half and limit carbohydrate availability. In addition, the study showed that the growth of young trees suffered, compromising the chances of survival into adulthood. Milligan’s results provide the first visualization of the dangers that invasive ground-nesting ants pose to plant physiology and growth in general.

Fat-headed ants move with remarkable speed, with each colony able to spread distances of 50 meters per year. “It’s crazy how much the landscape changes before your eyes,” Milligan said. “I can point to a tree and remember a time when it wasn’t overgrown, but now it is and half of it is gone, it’s just been blown to pieces.”

The new findings sound the alarm that globally, invasive ants have the potential to build vast networks of underground nests, impacting plant health over time. As this is the first documentation of this interaction, further experimentation is needed. “It’s possible it’s happening elsewhere, it’s just not something we’ve looked at under the microscope before,” he said.

Milligan hopes the study will encourage a new wave of research into the relationship between invasive ants and plant species. “I’m excited to see what other researchers might find if they apply the same tools we do to study other invasive ants – to see if this is some weird little phenomenon that just happened. in our system or if it’s a broader issue that we need to discuss in order to avoid negative effects on our environments,” Milligan said.