How Acacia Trees Prevent Elephant Attacks: With Armies of Ants

 

elephant eating a acaciaIt’s a classic David and Goliath story, except there are 90,000 Davids and they all have stings. On the African plains, the whistling-thorn acacia tree protects itself against the mightiest of savannah animals – elephants – by recruiting some of the tiniest – ants.

Ants on thornElephants are strong enough to bulldoze entire trees and you might think that there can be no defense against such brute strength. But an elephant’s large size and tough hide afford little protection from a mass attack by tiny ants.These defenders can bite and sting the thinnest layers of skin, the eyes, and even the inside of the sensitive trunk.Kenyan researchers found that ants are such a potent deterrent that their presence on a tree is enough to put off an elephants.

African plants have many defenses against elephants. Some try to match them for strength by developing thick buttresses. Others rely on physical defenses like thorns and poisons. Yet others abandon the fight and concentrate on being able to re-grow quickly. None of these measures is fool proof; despite these efforts, elephants frequently damage trees, severely and sometimes fatally.

ants on thornsThe whistling thorn acacia is a striking exception. Even in the heart of elephant country, it’s rarely touched and can grow in dense forests. It’s no coincidence that the whistling thorn has a partnership with ants. It provides them with homes in the form of swollen thorns, and food in the form of nectar. In return, the ants attack any invaders, regardless of their size.

Over a long period of time, these small differences can lead to substantial changes in the African landscape  The insect armies swarm intrusive browsers in exchange for housing and food. But according to new research in Science, it appears that without such browsing—a state of affairs the acacia might be thought to long for—the trees suffer.

Namibia; Namib Desert, Skeleton Coast, desert elephant (Loxodonta africana) eating bark of acacia tree
Namibia; Namib Desert, Skeleton Coast, desert elephant (Loxodonta africana) eating bark of acacia tree

Elephants are very effective at stripping trees’ bark and destroying them while feeding. “The number of elephants in the central highlands of Kenya has become high enough in recent years that we see severely elephant-damaged trees all over the place these days,” said study author Todd Palmer.
The researchers were intrigued though when they noticed that tree cover had only decreased in areas with sandy soil – not those with clay soil. In order to find out exactly what was putting the elephants off these trees, Professors Palmer and Goheen first tried stripping ants from the ant plants.
Elephants then became interested in eating the trees, but the ants came back – the more ants there were, the less elephants wanted to eat the trees.

The elephants wouldn’t even touch the branches with ants on – they could smell the ants and knew it would be painful to eat them” said Professor Jake Goheen, University of Wyoming
Whenever you create a disturbance in the tree canopy, the ants come and investigate. The elephants seem to be wary of getting bitten on the soft undersides of their trunks.
Elephant eating treeIn fable elephants are afraid of mice, but in reality they seem to be more afraid of insects. Previous studies have found that elephants are not only afraid of ants but also will run away from areas with bees, as soon as they hear them buzzing.

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