Oecophylla ants pushing montane birds higher up the mountains, finds study

A recent study from the Centre for Ecological Sciences (CES), Indian Institute of Science (IISc), has found that Oecophylla ants may be pushing montane birds higher up the mountains.

A recent study from the Centre for Ecological Sciences (CES), Indian Institute of Science (IISc), has found that Oecophylla ants may be pushing montane birds higher up the mountains.

According to the IISc, in mountainous regions, species diversity – the measure of how many different species are present – can vary with elevation due to environmental factors like climatic conditions.

However, the study by the CES team, has uncovered a different factor driving bird species diversity at mid-elevations: the presence of ants from the Oecophylla genus.

“In mountains, you often see hump-shaped patterns (of species diversity), and for a long time, people have been interested in why this happens. One of the mechanisms they did not think much about was biotic interactions like competition,” said Kartik Shanker, Professor at CES and co-author of the study published in Ecology Letters.

Oecophylla ants, known for their aggressive and dominant behaviour, are voracious predators of insects at the bases of mountains found in the paleotropics, covering Africa, Asia and Oceania. The researchers decided to test how the ants’ presence affects the diversity of insect-eating birds, especially at lower elevations.

A previous study led by co-author Trevor D. Price, Professor at the Department of Ecology and Evolution, University of Chicago, showed that the presence of Oecophylla ants at the base of the eastern Himalayas decreased the density of insects and might therefore have an effect on the presence of insect-eating birds. In the current study, the team wanted to see if this pattern was more widespread among other insect-eating species as well.

Led by Umesh Srinivasan, Assistant Professor at CES, the researchers used existing datasets with information about bird species observed at various elevations across different mountain ranges. They categorised the birds into dietary guilds – groups of species with similar dietary requirements, such as insectivores and omnivores.