What Happens When You Turn Up the Heat on Ants?
Published by the Natural Resources Defense Fund
Lauren Nichols
“Close the door! We’re not paying to heat the whole neighborhood!”
Moms and dads have been screeching that for decades, but what would happen to your community if you did pump out hot air until temperatures rose as high as climate scientists say they will by 2070?
This kind of question is tough to answer. After all, the heat-your-whole-street experiment is sort of impossible (and Mom and Dad have already made it clear they won’t fund it). But you can heat an ant’s entire neighborhood, and for the past five years, scientists working in North Carolina and Massachusetts have been doing just that—forcing out air that’s 1.5 to 5 degrees Celsius warmer than average over small patches of forest. Why? To see how heat affects the day-to-day toils of ant communities.
Lauren Nichols
Ants make up an enormous proportion of the creepy crawlies you’ll find in the dirt between Massachusetts and North Carolina—more than half, in fact. And though we don’t always appreciate them, these six-legged creatures are responsible for so many crucial ecosystem services, from seed distribution and soil aeration to decomposition and pollination. Each species has its role, which includes keeping the other ant populations in check.
More than 60 different species of ants are foraging on the floors of America’s eastern forests, and competition among them is usually pretty intense, says Sarah Diamond, an ecologist at Case Western Reserve University in Ohio and lead author of a study published in Science Advances in October. Under normal conditions, different colonies come and go, playing a sort of musical chairs game among nest sites. Scientists call this “turnover.”
In an overheated forest, according to the research, this turnover grinds to a halt.
“Instead, we see that heat-loving, thermophilic ant colonies are staying put in the nest sites for much longer periods of time, forcing the remaining ant species to seek alternate nest sites,” Diamond says. “If they can.”
What might this mean in a real forest setting? Well, the unsatisfying answer is that it’s complicated. You could argue that climate change will be good for some species, like Crematogaster lineolata, a tiny but aggressive ant native to much of the middle and eastern United States. Diamond and her colleagues found that as they increased the temperature in sections of Duke Forest in North Carolina, C. lineolata was more and more likely to be the species occupying the nests.
But this good fortune did not extend to the C. lineolata ants of New England. Up at Harvard Forest in Massachusetts, a species called Temnothorax longispinosus and ants in the genus Camponotus were the ones with the most to gain from rising temperatures. Down south, Aphaenogaster experienced increased homelessness, while up north it was Myrmica.
For every species that won in the scientists’ artificially warmer world, there were others that lost. But the researchers can’t definitively say that the losers just can’t stand the extra heat. It’s more likely that the heat is influencing the behavior of some species, with ripple effects in the larger ant community.
For example, C. lineolata is a bit of a bully, and when given the chance, it will beat up on Aphaenogaster, an important seed disperser. The latter might be capable of doing fine in warmer climes, but they still end up losing because their mortal enemies are doing way finer. How this shifting relationship could affect the way seeds are distributed in the forest and the succession of plant growth that follows is anybody’s guess. And that’s just one interaction among many in the ant kingdom.
“I would say that the merit of this work is very high,” says Kaitlin Baudier, a PhD candidate at Drexel University, in Philadelphia, who studies the thermal biology of army ants and how they may respond to climate change.
Most studies look at current distributions of organisms and the temperatures they can tolerate and then apply these to future predictions of climate change, Baudier says. What makes the recent study unique is that the researchers didn’t just make predictions based on hypothetical models. They made climate change actually happen for these ants and then watched as they responded over the course of five years.
The overall message these arthropods are sending us is that we can’t just look at how climate change affects any one species. Every ecosystem, from the leaf litter to the canopy, is a mess of tangled yarn. You can’t pull one species’ string without knotting or loosening whole clumps of others. For her next study, Diamond will be teasing apart some of these finer threads. Could seeds hitch rides on something else? Does C. lineolate have a backup plan in the warming north? Will T. longispinosus rule the day? Stay tuned.
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