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 fossilised 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. 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.
Savvy Soumya Misra