Invader Ants Hurting Ecosystems, Economies

By John Roach
for National Geographic News
November 9, 2001

When merchant ships embarked from the shores of Brazil and Argentina in the early 1900s to carry coffee and sugar to South Africa, North America, and the Mediterranean, they carried a mischievous stowaway: Linepithema humile.

The tiny black insect, better known as the Argentine ant, used burgeoning global trade to invade ant communities around the world. Scientists are just now beginning to tally the damage. The reports are grim. Entire native ant populations have disappeared.

To examine the consequences of such invasion on mutually beneficial relationships between ants and plants native to an area, Caroline Christian, a biology student at the University of California at Davis, looked at the biologically rich fynbos shrublands of South Africa.

Her research, reported in the October 11 issue of Nature, shows that when key beneficial species are removed by an invader, the destructive effects ripple through the entire ecosystem.

Fire and Seeds of Regeneration

Wildfires sweep across the fynbos once every 15 to 30 years, killing most mature plants and starting a cycle of regeneration. New plants grow from seeds that native ants have buried in the ground.

The seeds have fatty coatings, called elaisomes, which are highly sought-after sustenance for ants. When the ants eat this coating, the seeds are left unharmed. To protect this source of food from rodent seed predators, native ants bury the seeds.

The relationship is mutually beneficial: The ants are fed, and plants will regenerate in the event of a fire because their seeds have been buried out of harm's way.

Rodents quickly eat any seeds that are left unburied. Christian hypothesized that when fire sweeps fynbos areas that have been invaded by Argentine ants, certain plant species whose seeds are normally dispersed by native ants would not regenerate.

Controlled Burn

Continued on Next Page >>


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