The ants that defeated the lions

This is an ensemble film where there are ants that protect some trees from huge elephants and in return they receive shelter.

In the shade of the whistling thorns (a type of acacia), the lions stalked the zebras, their favorite prey, which meant that they did not need to attack the imposing buffaloes, which lived peacefully in this part of the African savanna.

But a few years ago, another species of ants called lionesses arrived at Ol Pejeta Park in Kenya - curiously - and have turned the ecosystem upside down.

After exterminating the native ones, the acacias were left without their protectors, the pachyderms destroyed them and the cats lost the parapet from which to ambush zebras that can no longer hunt.

In the end, in this story, those who lose are not so much the

kings of the jungle

as the buffaloes, which have come to represent almost half of the lions' menu.

The whistling hawthorn (

Acacia drepanolobium

) is a myrmecophyte plant, that is, it lives in association with a colony of ants, in this case with the

Crematogaster mimosae

.

The symbiotic relationship between acacia and insects is what ecologists call foundational mutualism, because they are at the base of the entire ecosystem.

Trees have evolved to develop specific organs where insects raise their nests.

They also exude nectar out of flowers for their hosts.

In return, the ants fiercely defend them from the elephants, which make up 70% of the megaherbs in the park.

Their weapons?

The jaws and formic acid they release into the elephants' very sensitive trunk, but also into the entire mouth and eyes.

Despite the unequal nature of the battle, the defense works, as the images before and after the invasion show.

The dominant landscape in Kenya's Ol Pajete Reserve is savanna dotted with acacias such as the whistling hawthorn, which accounts for up to 90% of the forest cover.Patrick Milligan

These acacias, the base of the ecosystem, are also key at its peak.

The savannah is a landscape of fear in which the game between life and death, between predators and preyed upon, depends on visibility.

In the Ol Pejeta park (famous for housing the last two northern white rhinos and being the scene of their attempted recovery), lions take advantage of the hissing hawthorn to stalk the zebras, which seek the more open spaces the better.

Equids accounted for two-thirds of the felines' diet until

the bad news

in the movie arrived.

“We started detecting them around 2014, but they had already been there for a while, maybe more than a decade.

They are very small, so they can go unnoticed if you are not looking for them,” says Todd Palmer, an ecologist at the University of Florida (United States) and senior author of this research.

Palmer has been working at Ol Pejeta since the beginning of the century and had published several works on the mutually beneficial relationship between acacias and their ants.

Therefore, his concern grew as he saw how the ant lions (

Pheidole megacephala

) were taking over one acacia tree after another.

These ants are among the 100 most harmful invasive species on the planet.

And they have that well-earned reputation.

When they reach a hissing thorn, they kill rivals and eat their eggs, pupae and larvae, destroying the anthill, although they are much smaller than

C. mimosae

.

“When they appeared, none of us noticed because they are not aggressive towards large animals, including people.

Now we see that they are transforming landscapes in very subtle ways, but with devastating effects,” adds Palmer.

Several elephants wander through an area of ​​Ol Pejeta that was invaded by ant lions, which left the acacias at the mercy of the pachyderms. Brandon Hays

Once the defenders have been exterminated, the ant lions bore holes in the ground under the acacia where they create their anthill and ignore the fate of the tree, which is left defenseless against the browsing of the elephants.

These huge herbivores are not conservative and, without formic acid and bites to prevent it, they do not limit themselves to leaving the tree without leaves, they destroy it.

The consequence has been that, in the last decade, the landscape has been cleared.

Ecologists were clear that this was going to have consequences at the highest level.

To investigate, they fenced several plots with electrified wire fences, both in areas with invaded and invasive whistling thorns, and followed the movements of six lionesses with GPS collars that belonged to as many prides whose population exceeds 80 felines.

For three years they analyzed their movements and the number of prey they hunted.

The results, now published in the scientific journal

Science

, show the chain reaction that can be caused by a tiny animal measuring just 2 millimeters (the workers, the soldiers reach up to 12), capable of forcing the king of the jungle to change prey. which it feeds on.

In the plots without fencing, but with invasive ants, many of the acacias have disappeared and visibility has almost tripled.

Unlike other ecosystems, the lions of Ol Pejeta do not pursue their prey.

They stalk and ambush her, taking advantage of the distortion of the scenery caused by the trunks and foliage of the trees.

But without them, the occurrence of captured zebras in areas invaded by ants 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 feline diet has dropped from 67% to 42%.

However, the lion population has not decreased.

The explanation seems to be in the buffaloes.

20 years ago, before the ant lions arrived, the cats did not hunt a single buffalo.

Now, they represent 42% of their menu.

Despite being three times smaller, the invasive ant lions rely on numbers to defeat their rivals.

They then eat the larvae, pupae and eggs, taking away all hope of recovery from the anthill.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 ant lions advance through Ol Pejeta at a rate of 50 meters a year.

At the other end of the ecosystem, the savanna's biggest predator has been forced to change prey.

In an email, Palmer recalls that “buffalo are very large, with males being twice the size of the largest zebra, and both males and females have horns that they can use to defend themselves, so they will always be prey.” formidable;

Whether lions will be able to continue hunting more buffalo without suffering the consequences is an unanswered question, for now.”

The ending of this film is yet to be decided.

The invasion of ant lions, introduced inadvertently by humans from the Indian Ocean islands, is a growing phenomenon throughout East Africa, a large region of hundreds of thousands of square kilometers in which between 70% and 90% of the vegetation cover is acacia species such as whistling hawthorn.

It is not known what consequences it could have if what is happening in Ol Pejeta is also happening in other parks and reserves.

In a commentary on the study, also published in

Science

, University of British Columbia (Canada) zoologist Kaitlyn M. Gaynor writes: “Ultimately, preserving healthy ecosystems requires not only preventing species extinction, but also to identify and preserve the most important interactions between species,” such as that of the whistling hawthorn and its protective ants.

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