This is an ensemble film where ants protect some trees from giant elephants and receive protection in return. In the shade of the whistling thorns (a type of acacia), the lions pursued the zebras, their favorite prey, so that they did not have to attack the imposing buffalo that lived peacefully in this part of the African savannah. But strangely enough, a few years ago, another species of ants called lionesses arrived in Ol Pejeta Park in Kenya and turned the ecosystem upside down. After the extermination of the locals, the acacias were left without a protector, the pachyderms destroyed them, and the cats lost the parapet from which they could attack zebras that can no longer hunt. Ultimately, in this story, it's not so much the kings of the jungle who lose, but rather the buffalo, which now make up almost half of the lion's menu.
The whistling hawthorn (Acacia drepanolobium) is a myrmecophyte plant, which means it lives in association with an ant colony, in this case with the Crematogaster mimosae. The symbiotic relationship between acacias and insects is called fundamental mutualism by ecologists because they form the basis of the entire ecosystem. Trees have evolved to develop special organs in which insects build their nests. They also release nectar from the flowers for their hosts. In return, the ants fiercely defend them from the elephants, which make up 70% of the megaherbs in the park. Your weapons? They release the jaws and formic acid into the elephant's very sensitive trunk, but also into the entire mouth and eyes. Despite the disparity of the battle, the defense works, as the images before and after the invasion show.
The predominant landscape in Kenya's Ol Pajete Reserve is savannah with acacia trees such as hawthorn, which make up up to 90% of the forest area.Patrick Milligan
These acacias, the basis of the ecosystem, are crucial even in its heyday. The savannah is a landscape of fear, where the game between life and death, between predators and prey, depends on visibility. At Ol Pejeta Park (famous for housing the last two northern white rhinos and the site of their attempted recovery), lions use the hissing hawthorn to stalk the zebras, who are even more eager to find open spaces. By the time the bad news hit in the movie, equines made up two-thirds of the cats' diet.
“We started detecting them around 2014, but they had been there for a while, maybe more than a decade. They are very small and can therefore go unnoticed if you are not looking for them,” says Todd Palmer, an ecologist at the University of Florida (USA) and lead author of this study. Palmer has worked at Ol Pejeta since the beginning of the century and has published several works on the mutually beneficial relationship between acacia trees and their ants. So his concern grew as he saw the antlions (Pheidole megacephala) taking over one acacia tree after another. These ants are among the 100 most damaging invasive species on the planet. And they have this well-deserved reputation. When they reach a hissing hawthorn, they kill rivals and eat their eggs, pupae and larvae, destroying the anthill despite being much smaller than C. mimosae. “When they appeared, none of us noticed because they are not aggressive towards large animals, including humans. Now we see them changing landscapes in very subtle ways, but with devastating effects,” adds Palmer.
Several elephants wander through an area of Ol Pejeta that has been infested with antlions, leaving the acacia trees at the mercy of the pachyderms. Brandon Hays
Once the defenders are eradicated, the antlions drill holes in the ground beneath the acacia tree, where they build their anthill, ignoring the fate of the tree, which is defenseless against the elephants' bite. These giant herbivores are not conservative and without formic acid and bites to prevent them, they do not limit themselves to leaving the tree without leaves, they destroy it. The result was that the landscape was cleared over the last decade. It was clear to the ecologists that this would have consequences at the highest levels. To investigate this, they surrounded several plots with electric wire fencing, in areas with both invaded and invasive whistling thorns, and tracked the movements of six lionesses with GPS collars who belonged to as many prides whose population includes more than 80 cats. For three years they analyzed their movements and the number of prey they hunted.
The results, now published in the journal Science, show the chain reaction that a tiny animal measuring just 2 millimeters (the workers, the soldiers reach up to 12) can set off, forcing the king of the jungle to change his prey. which it feeds on. In the plots without fences but with invasive ants, many acacias have disappeared and visibility has almost tripled. Unlike other ecosystems, the lions of Ol Pejeta do not pursue their prey. They pursue and ambush them, taking advantage of the distortion of the landscape caused by the trunks and leaves of the trees. But without them, the incidence of trapped zebras in ant-infested areas was almost three times lower than in areas where there were still hissing thorns free of the pest. Since 2003, the proportion of zebras in the park's cat diet has fallen from 67% to 42%. However, the lion population has not declined. The explanation seems to lie in the buffalo. 20 years ago, before the antlions came, the cats didn't hunt a single buffalo. They now make up 42% of their menu.
Despite being three times smaller, the invasive antlions rely on their numbers to defeat their rivals. They then eat the larvae, pupae and eggs, depriving the anthill of any hope of recovery.Patrick Milligan
“Nature is intelligent and creatures like lions tend to find solutions to the problems they face,” says Palmer, “but we still don’t know what will happen after this profound change in their hunting strategy; “We want to know how this story ends.” The antlions advance through Ol Pejeta at a speed of 50 meters per year. At the other end of the ecosystem, the savanna's largest predator was forced to change its prey. In an email, Palmer reminds that “buffalo are very large, with males being twice the size of the largest zebra, and both males and females have horns to defend themselves, so they will always be prey .” impressive; Whether lions can continue to hunt more buffalo without suffering the consequences is, for now, an unanswered question.”
The ending of this film has not yet been decided. The invasion of antlions, introduced unintentionally by humans from the Indian Ocean islands, is a growing phenomenon throughout East Africa, a large region of hundreds of thousands of square kilometers where between 70 and 90% of the vegetation cover is Acacia species such as whistling hawthorn . It is unknown what the consequences might be if what happens in Ol Pejeta happens in other parks and reserves. In a commentary on the study, also published in Science from the University of British Columbia, Canada, zoologist Kaitlyn M. Gaynor writes: “Ultimately, maintaining healthy ecosystems requires not only preventing species extinctions, but also identifying and preserving them of the most important interactions between them.” Species”, such as that of the whistling hawthorn and its guardian ants.
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