By replacing native ants, the tiny black Argentine ant — a well-known household pest — could be disrupting natural ecosystems. A study by UC Davis graduate student Caroline Christian, published in Nature (October 2001), has shown that when key beneficial species are removed by an invading ant, the destructive effects can reverberate through the ecosystem.

Research conducted in the fynbos shrub-lands of South Africa, below, which is similar to California chaparral in appearance, demonstrates the important role that natives ants play in regenerating vegetation after a fire.

Christian, who is affiliated with the UC Davis Center for Population Biology, studied the fynbos shrublands of South Africa, an area similar in climate and vegetation to the chaparral of California. Wildfires sweep the fynbos every 15 to 30 years, killing most mature plants; new plants grow from seeds buried in the ground by native ants. Christian found that when Argentine ants displace native ants, plants that depend on those ants to bury their seeds do not regenerate after fire.

Seed burial by ants is key to survival for about a third of fynbos plant species, Christian said. When fresh seeds fall, ants are attracted to them and carry them off to bury in their nests. Different ant species specialize in seeds of different sizes: Ants that work cooperatively deal with bigger seeds, while ants that tend to work alone bury smaller ones. If the seeds are not picked up quickly, virtually all are eaten by rodents.

After controlled burning, fynbos areas invaded by Argentine ants showed a tenfold drop in the number of new plants from large-seeded species, compared to uninvaded areas, Christian said. Small-seeded species were much less affected.