WSB Study: Fire ants could be exacerbating gopher tortoise threats

By Joshua Rapp Learn

A baby gopher tortoise in the longleaf ecosystem. ©Randy Browning/USFWS

Gopher tortoise populations facing threats from habitat loss and depredation could be feeling extra heat from invasive fire ants.

“I think fire ants have the potential to do some serious damage to gopher tortoise populations in the right conditions,” said Michelina Dziadzio, who was a master’s student at the University of Georgia while working on a recent study published in the Wildlife Society Bulletin.

Gopher tortoises (Gopherus polyphemus) are recognized in two distinct populations by the U.S. Fish and Wildlife Service. The population west of Mobile, Alabama, is listed as threatened under the Endangered Species Act. Dziadzio and the other researchers focused on the eastern population, currently a candidate for federal listing and a threatened species according to Georgia state lists.

Fire ants. ©Marufish

Fire ants. ©Marufish

The tortoises face threats like the loss of their fire-dependent longleaf pine ecosystems as well as depredation from species such as raccoons (Procyon lotor) and non-native nine-banded armadillos (Dasypus novemcinctus) — the primary predator of tortoise eggs in the Joseph W. Jones Ecological Center near Newton, Georgia, which served as the study area. But fire ants (Solenopsis spp.) have also been found to depredate turtle nests.

Gopher tortoises tend to live in burrows in longleaf pine forests. The females lay their eggs in the soil that piles up at the entrance as a result of their digging. The loose quality of the soil may provide the eggs with extra incubation, but it’s also the ideal place for fire ants to create the mounds where they live.

“Fire ants like a softer soil and they like open areas where there isn’t a lot of vegetation,” Dziadzio said.

She and her coauthors wanted to see if the ants showed some preference for these turtle areas under different conditions. They tracked 14 nesting sites throughout incubation after egg laying and found that the ants made mounds near nine of the nests, always near the beginning of the incubation period. While they can’t be sure, Dziadzio said that this could mean that the ants might smell the mucus that coats the eggs and other related moisture soon after laying.

While the ants can’t penetrate egg shells in good condition, they can wipe out an entire nest if they are around when the shells begin to hatch as they can enter the shells and begin devouring young turtles before the reptiles can escape.

This doesn’t always happen though. Only one of the nests that the researchers followed was wiped out by ants, while small mammals destroyed six of the others.

“If they’re in the foraging range of fire ants, they have the chance to be depredated by fire ants,” Dziadzio said.

The researchers aren’t sure what kind of effect the fire ants are having on tortoises at a population level, though, since most tortoise hatchlings rarely live until adulthood anyway.

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society.

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