The ant's travelogue

By Savvy Soumya Misra
Published: Tuesday 30 June 2009

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50 million years ago, it hiked all the way from Europe to Australia in search of some warmth

ANTS were dominant members of the earth's ecosystem about 100 million years ago. Although humans were not around, the ants worked on the soil making it fit for agriculture, drove away pests, killed weeds, dispersed seeds and domesticated aphids for food. A change in the environment 50 million years ago brought their numbers down drastically. It was climate change even then but with one difference the earth did not get warmer, it cooled down.

Rob Dunn of the North Carolina State University, usa, and his team of 26 researchers from eight countries created a Global Ant Community Database which had about 1003 local ant communities from over 3,000 sites.The scientists then collected data on the fossilized remains of ants, the present climate, glacial history of sites and temperature change since the Ecocene period 50 million years ago. Thereafter emerged a global pattern on the biological diversity of ant communities.

A sudden drop in temperatures was found to be behind large-scale extinctions of ant species in the northern hemisphere where the cooling effect was more pronounced. Temperature and precipitation was greater in the southern hemisphere. As ants prefer dry and warm conditions, they continued to survive in the south. Those who could, particularly the ground-foraging ants, migrated to the south. One was the weaver ant, now thriving in Australia. The team traced its origin back to Europe.

"Ants diversified most when the planet was warm and during the Ecocene era, the world was largely tropical and bubbling with ants. Due to a complex function of long-term climate cycles, the northern hemisphere cooled more than the southern hemisphere and so there was more extinction there," explained Dunn in the paper published in Ecology Letters (Vol 12, issue 4).

It is clear now why Australia has more ant species than the entire northern hemisphere put together. But very few species migrated. After all, as Dunn pointed out, it is a long walk from Europe to Australia if the creature in question is just half a centimetre long.

The study makes a strong link between ants and climate but it has its limitations. "There were differences in sampling among sites, difficulties in measuring climatic data and differences in how to group the ants," said Dunn.

Having more ants in one's backyard has its pros and cons. Ants are good at pest biocontrol and scavenging wastes. "The weaver ant helps in farming by eating pests. Imagine what it could do for Europe had it not moved south," said Dunn. But if the ants that increase are invasive, like fire ants, there is a problem. Fire ants swarm on electrical equipment, damaging them severely.

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