Tiny ants have a big impact on the hunting behavior of lions

An invasive species known as the big-headed ant is subtly but significantly altering the dynamics of a well-established ecosystem and the lions that live there, according to a new study from the University of Florida.

The research, led by Professor Todd Palmer, reveals that this seemingly inconspicuous ant is upending the hunting patterns of one of the world’s most formidable predators, the African lion, particularly in its pursuit of zebra prey.

The study is a culmination of over three decades of rigorous research. The team used a combination of hidden camera traps, collared lions tracked by satellites, and statistical modeling. 

The experts have shed new light on the complex interplay among different species – ants, trees, elephants, lions, zebras, and buffaloes – in the Ol Pejeta Nature Conservancy in central Kenya.

Mutually beneficial relationship

Historically, the acacia trees in this region have enjoyed protection from leaf-eating animals, courtesy of a mutually beneficial relationship with a native ant species that nests in the trees’ bulbous thorns.

These ants fiercely guard the trees against large herbivores such as elephants and giraffes — a phenomenon known as mutualism. 

Earlier studies by Palmer in the early 2000s began unraveling the complexities of this symbiosis. The experts discovered the ants’ role in stabilizing tree cover, thus enabling acacia trees to thrive amidst numerous large plant-eating mammals.

“Much to our surprise, we found that these little ants serve as incredibly strong defenders and were essentially stabilizing the tree cover in these landscapes, making it possible for the acacia trees to persist in a place with so many big plant-eating mammals,” said Professor Palmer.

Ants, lions, and ecosystems

However, the introduction of the invasive big-headed ants has triggered a cascade of ecological consequences.

Unlike their native counterparts, these invasive ants do not defend the acacia trees from larger herbivores. 

This invasion has led to a significant reduction in tree cover, as elephants, no longer deterred by ant protectors, freely feed on the acacias.

The sparse tree cover impairs the lions’ ability to effectively ambush zebras, their preferred prey, as they rely heavily on the camouflage and strategic advantage provided by dense vegetation.

“These tiny invaders are cryptically pulling on the ties that bind an African ecosystem together, determining who is eaten and where,” said Professor Palmer.

A transformative force

The invasion of big-headed ants, which occurred around 15 years ago, went largely unnoticed due to their non-aggressive nature towards larger animals, including humans.

However, their presence is now recognized as a transformative force reshaping the landscape with far-reaching implications.

“Oftentimes, we find it’s the little things that rule the world,” said Palmer. “These tiny invasive ants showed up maybe 15 years ago, and none of us noticed because they aren’t aggressive toward big critters, including people. We now see they are transforming landscapes in very subtle ways but with devastating effects.”

Adapting to these environmental changes, lions have begun shifting their hunting focus towards buffalo, a more challenging and formidable prey given their larger size and tendency to move in groups.

This shift in the lions’ hunting strategy raises concerns and curiosity about the potential long-term ecological consequences.

“Nature is clever, and critters like lions tend to find solutions to the problems they face, but we don’t yet know what could result from this profound switch in the lions’ hunting strategy. We are keenly interested in following up on this story,” said Professor Palmer.

Protecting lions from ants

For the investigation, Professor Palmer collaborated with Jake Goheen from the University of Wyoming, Corinna Riginos from The Nature Conservancy, and Douglas Kamaru of the University of Wyoming.

The team plans to explore possible interventions to mitigate the loss of tree cover. The interventions could include temporary fencing to protect trees from large herbivores.

“These ants are everywhere, especially in the tropics and subtropics. You can find them in your backyard in Florida, and it’s people who are moving them around,” said Professor Palmer.

“We are working with land managers to investigate interventions, including temporarily fencing out large herbivores, to minimize the impact of ant invaders on tree populations.”

In an era where advanced technologies like AI-powered data collection are gaining prominence, Professor Palmer emphasized the enduring value of traditional, field-based research. 

“There are a lot of new tools involving big data approaches and artificial intelligence that are available today, but this study was born of driving around in Land Rovers in the mud for 30 years.”

The research is published in the journal Science, and was supported by the National Science Foundation. 

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