European fire ants spell trouble for North American forests

Chuck Bednar for redOrbit.com – Your Universe Online
Invasive species are often bad news for the local environment, but new research suggests that the European fire ant could be double trouble for forest ecosystems in eastern North America.
In a new paper, evolutionary biologists from the University of Toronto report that the European fire ant (Myrmica rubra) can not only invade people’s backyards and deliver a nasty sting in the wrong circumstances, but it is also helping spread the seeds of an invasive plant seeds.
“Ecologists think invasive species might help each other to spread, but there are few good examples. They talk about ‘invasional meltdown,’ because ecosystems could be very, very rapidly taken over by invasive species if invaders help each other out,” explained Megan Frederickson, one of the authors of a study that will be published Wednesday in the journal Proceedings of the Royal Society B. “Our results suggest that invasional meltdown could be happening right under our noses, here in Ontario.”
Frederickson, Kirsten M. Prior, Jennifer M. Robinson and Shannon A. Meadley Dunphy, all from the university’s Department of Ecology and Evolutionary Biology, created artificial ecological communities inside 42 small plastic swimming pools. These communities, also known as mesocosms, were created a field station, the Koffler Scientific Reserve at Jokers Hill.
Each of the pools was filled with soil, and the researchers planted four species of spring wildflowers – three native species (sharp-lobed hepatica, Canadian wild ginger and bloodroot) and one invasive species (greater celandine). Next, they collected colonies of either the European fire ant or a native woodland ant, adding them to the pool. Each ant picked up and relocated seeds of their respective plant species as the study authors monitored their activity.
“The pools with the invasive ant were overrun by the invasive plant, but pools with the native ant had lots of native plants,” Prior said. “Unfortunately, as a result of humans rapidly moving species around the globe through trade and traffic, most ecosystems are now home to numerous invasive species.”
“Our finding that multiple invasive species can accelerate invasion and cause ecosystems to become dominated by invasive species is a troubling one,” she added. “Invasive species are a leading threat to natural ecosystems, and can have impacts on society. Research on how ecosystems become invaded and the consequences of invasion is important. It sets us on the right path to develop solutions to reduce the spread and impact of these harmful species.”
The findings contradict previous research which found that invasive ants tended to be poor seed dispersers in comparison to their native counterparts. The University of Toronto team found that both native and invasive ants had a strong but divergent impact on plant communities, as the invasive plants dominated in the presence of the invasive ant and the native plants dominated in the mesocosms infested by native ants species.
“Community changes were not due to preferences for coevolved partners: variation in functional traits of linked partners drove differences. Here, we show that strongly interacting introduced mutualists can be major drivers of ecological change,” the authors wrote. Their research was funded by the Natural Sciences and Engineering Research Council and the Ontario Ministry of Economic Development and Innovation.
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