Ants forecast forests’ future

June 28th, 2010

Ants and other insects may not be the first things you spot on a walk in the woods, but N.C. State biologist Rob Dunn believes they have something important to say about the future of forests under climate change.

In forests in North Carolina and Massachusetts, Dunn and his colleagues built a series of 15-foot-wide enclosures, warmed to simulate temperature increases predicted for the coming decades.

The enclosures are part of a five-year, $3 million study funded by the U.S. Department of Energy to forecast the effects of rising temperatures on Eastern forests and the creatures that live there. The NCSU-led team is collaborating with researchers at the University of Tennessee, Harvard University and the University of Vermont to see if predictions for plants and animals are likely to come true.

Average annual temperatures in the Southeastern United States have risen by 2 degrees Fahrenheit since 1970 and could rise by up to 10 degrees before the end of the century, according to the U.S. Global Change Research Program.

“Some models predict that in 2100, the climate of Massachusetts will resemble that of North Carolina, and that of North Carolina will resemble Central Mexico,” Dunn said.

To forecast how ants and other forest insects might respond to a warming world, Dunn and his colleagues have spent the past two years building a dozen open-top enclosures in a part of the Duke Forest, an expanse of hardwoods and pines in Orange County.

Inside each octagonal enclosure lies an area the size of a living room, walled off with translucent plastic. The enclosures are heated to temperatures predicted for 2025, 2050 and 2100.

“We’re simulating the future and seeing how it plays out,” Dunn said.

A micro-world of creatures

Site manager Mark Boudreau crawls into one of the enclosures. Moisture and temperature sensors poke out of the understory, while a slow pulse of warm air blows in through clear plastic tubes.

“If you hold your hand under these, you feel warm air seeping out,” Boudreau said.

Buried under logs and leaf litter lies a micro-world – hundreds of red, black and brown ants crawl in and out of the enclosure as they forage across the forest floor. “So far we’ve found 29 ant species across the entire site,” Boudreau said.

Ants may seem like trivial players, but they play a big role in maintaining forest health. Representing 40 percent of the animal biomass in many forests, they mix and aerate the soil and recycle nutrients. More than one-third of forest flowers rely on ants to disperse their seeds.

“The seeds of many of our most spectacular spring flowers, such as bloodroot and trillium, are dispersed by ants,” said project investigator Nicholas Gotelli of the University of Vermont.

As winters warm and seasons shift, many species might be on the move. The two sites near Hillsborough and Harvard Forest in Massachusetts represent the southern and northern range limits for many plant and animal species, Dunn said.

Many species are making their way into areas where once they were unable to survive. That means forests are likely to support a different mix of species in the future than they do today.

Invasive fire ants spreading

Some new neighbors are less welcome than others.

“The South American fire ant is now found throughout the Southeastern U.S., and the European fire ant is beginning to bother picnickers and homeowners in Maine and Massachusetts,” Gotelli said.

As foreign pests expand their range, they can displace native species that play vital roles as partners for other forest plants and animals.

“All too often the invasive ants displace the native ants, but they don’t perform the critical functions that native ants provide,” said co-investigator Nathan Sanders of the University of Tennessee.

Dunn and his collaborators are taking a monthly census of the species in the enclosures at each site to document changes in where ants live and how they forage.

Preliminary experiments in smaller plots suggest that even moderate warming can have a big effect.

“We did a different experiment with one degree of warming, and saw almost a doubling of ant abundance in just three months,” Dunn said.

Ants in the lab

Back in the lab, Dunn takes a glass-topped case from a shelf to reveal hundreds of ants mounted on tiny pins, neatly labeled and arranged in rows.

“In our preliminary experiment, this particular group became much more common,” he said, pointing to an inconspicuous ant called Crematogaster lineolata.

The study’s findings are important not just because ants are a fundamental part of healthy forests, said Dunn, but also because they might function as an early warning system for environmental threats to human beings.

“Ants and other social insects can serve as a model of how societies in general – be they human or insect – respond to environmental change,” Dunn said.

“Ants are widely used as indicator species – as go ants, so go other species,” wrote co-investigator Aaron Ellison and post-doctoral researcher Shannon Pelini of Harvard University.

As the researchers continue studying ants, they are also looking at how entire insect communities – not just ants – respond to warming. This summer the group will study beetles, millipedes, wasps, flies, moths, termites, roaches and other small creatures – some beneficial, some problematic, but most just doing the work they have long done to persist.

Whether they be lice, dust mites or centipedes, Dunn admits to having a fascination with creatures that give most people the creeps.

“Most animals on earth are insects,” Dunn said.

“They’re the ones that carry disease, but they also pollinate our crops.

“The consequences of climate change that have the most immediate effects on us are likely to be mediated by these smaller creatures that many people don’t like as much.”

Many people, that is, aside from Dunn.

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