Lions certainly deserve their prestige as emperors of the African savanna, but they’ve recently been humbled by a tiny, pesky troublemaker: ants. A team of researchers noticed that the invasive big-headed ant species has been putting a damper on lions’ predation patterns by inadvertently assisting their main prey, zebras.
Researchers led by University of Wyoming Ph.D. student Douglas Kamaru spotted this occurrence at Kenya’s Ol Pejeta Conservancy. The results, published in Science, show a domino effect that leaves lions with the short end of the stick.
Invasion of the Big-Headed Ants
It all started when big-headed ants — likely coming from on an island in the Indian Ocean — pervaded East African environments with whistling-thorn trees, which have a special, symbiotic relationship with native ants.
The trees provide nectar and shelter for native ants, and to return the favor, these ants protect them from animals looking to take a bite to eat; whenever herbivores try to eat from the tree, the ants start biting and emitting formic acid to stave them off. Elephants in particular take this as a sign to steer clear of the ant-ridden tree.
The invasive big-headed ants throw a wrench in these established ecosystems as they kill the native acacia ants. The trees consequently lose their mini defense system, inviting herbivores to consume them. As a result, the trees are broken at a rate five to seven times higher than the rate recorded in areas not invaded by big-headed ants. The loss of trees means lions have less cover to hide behind, making it impossible for them to successfully ambush zebras.
“We show that the spread of the big-headed ant, one of the globe’s most widespread and ecologically impactful invaders, has sparked an ecological chain reaction that reduces the success by which lions can hunt their primary prey,” the researchers wrote.
The team studied lion and zebra activity in areas with and without big-headed ants. They found that the ant invasion caused lions to kill zebras less because of the increased openness across the landscape.
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Switching To New Prey
Although the lions in this region have been increasingly deprived of zebras to hunt, they have adapted by targeting African buffalo instead. The buffalo are larger than zebras and harder to kill, but the lions affected by the ant invasion appear to have switched their diets without much trouble; the lion population in this part of East Africa has not declined according to the researchers.
However, as more lions in the region are forced to hunt buffalo in lieu of zebras, the size and composition of lion prides could experience significant shifts.
“The role of behavioral adjustments in underlying the population stability of lions, plus the degree to which such stability can be maintained as big-headed ants advance across the landscape, remain open questions for future investigation,” the researchers concluded in the study.
As big-headed ants infiltrate ecosystems in Africa, a whole host of other plant and animal species could be negatively affected. For now, the hope is that their spread can be suppressed in some way, possibly by targeting the queens of the ant colonies.
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