How a colony of baby ants affects local trees, elephants, lions, zebras, and buffalo.
You may have heard stories about elephants scared of baby mice. Unfortunately, this is a rumor. However, a recently published study showed that tiny ants can completely disrupt the lives of lions. What's going on?
Tacit collaborators
In the tens of thousands to hundreds of thousands of square kilometers that stretch across East Africa, the Vachellia drepanolobium is almost the only tree species. The reason for its name "sickle pod" is that its pods are curved, like a fiery red sickle.
Another peculiarity of the sickle is that it is covered in spikes, some of which swell into hollow balls at the base. This particular structure serves as a shelter for many ants, who create holes in and out of these balls and burrow into them. When the wind blows through the empty ball with holes, the sickle acacia makes a whistle-like sound, which is why some people call it the "whistling-thorn tree".
The inhabitants of the Acacia Spheres are mainly local Crematogasters, who can enjoy a buffet of extrafloral nectar glands on the petioles of the lower petioles of the Acacia. However, the bellied ants live on food for many other local animals, especially large herbivores such as the Nubian giraffe (Giraffa camelopardalis) and the African savannah elephant (Loxodonta africana), which feed on the sickle pods.
Naturally, bellied ants can't tolerate the gnawing of their beautiful home, so when elephants come to feed, they immediately release pungent pheromones to notify their partners of the threat. Worker ants that receive the signal will quickly assemble and rush to the mucous membrane of the elephant's mouth and nose, biting frantically while releasing formic acid. The siege of dozens or even hundreds of ants caused the elephants to be in great pain, and they had to go home.
In this way, a good mutually beneficial symbiotic relationship was formed between the bellied ant and the sickle acacia. Elephants also learn to protect themselves in the process: they first sniff (perhaps pheromones) with their noses, determine the species and density of ants that inhabit the acacia, and then decide whether to lower their mouths. As a result, the sickle pods, inhabited by the most ferocious and dense ants, are best protected and survive in the savanna.
Invasion of brown big-headed ants
However, since the early 2000s, this mutually beneficial and peaceful life has been shattered when a colony of brown big-headed ants (Pheidole megacephala) that came out of nowhere (but is likely related to the global movement of people and goods) invaded the savanna in Laikipia County in central Kenya. As one of the most feared invasive species in the world, the brown big-headed ant has brought extinction to the bellied ant. Giant colonies of brown big-headed ants not only kill the adult bell-bearers, but also eat the eggs, larvae, and pupae of the bellied-bellied ants.
In just 10 years, the brown big-headed ant has wiped out almost all the belly-raising ants that parasitize the falcyte acacia in the area. However, unlike the bellied ant, the brown ant does not have a mutually beneficial symbiotic relationship with the sickle pod. They live underground and do not actively attack large animals.
As a result, the balance between the acacia, the bellied ant and the elephant was upset, and a large number of the acacia were eaten by elephants, and their numbers rapidly declined. The data showed that in the area invaded by brown big-headed ants, the elephant ate and knocked down the falcous acacia at a rate of 5~7 times that of the uninvaded area.
The lion who was forced to change
However, the invasion of brown big-headed ants has not only changed the lives of bellied ants and elephants, but also set off an even bigger storm. The once widespread acacia not only sheltered the bellied ants, but also served as a shelter for many animals. For example, lions often need to hide in these sickle acacias, observe them, and then swoop in before ambushing prey such as the plains zebra (Equus quagga).
Researchers from the University of Wyoming in the United States, who conducted a three-year study here, found that the average visibility in the area that was not invaded by brown big-headed ants was 18 meters, while the average visibility in the invaded area reached 48 meters, an increase of 2.67 times. Researchers speculate that the disappearance of such bunkers is likely to affect lion predation.
And so it turned out. The invasion of brown big-headed ants increases the visibility of the area, and the higher the visibility of the area, the less likely the zebra is to be preyed upon by lions. Compared with the area invaded by the brown macrocephalic ant, the mortality rate of zebras in the area not invaded by the brown macrocephalic ant was 2.87 times higher. From 2000 to 2020, the proportion of zebras killed by lions has dropped from 67% per year to 42% per year.
Since they are difficult to hunt, do these lions migrate to areas that are not invaded by brown big-headed ants because they can't find food in the open area? Curiously, the researchers found no signs of this, and the lions appear to be equally active in the two areas. What is even more strange is that the number of lions here has not decreased due to the invasion of brown big-headed ants in the past decade or so.
The researchers speculate that since the lions are much less likely to successfully hunt zebras here, but their populations are not, they must have some other way of supplementing their food sources. The researchers found that as the coverage of the falcous acacia decreased year by year, the annual mortality rate of zebras decreased year by year, and the proportion of African buffalo (Syncerus caffer, another ungulate wild animal commonly hunted by lions) killed by lions began to increase year by year, jumping from 0% in 2000 to 42% in 2020.
In general, large mammals like lions are less likely to change prey, and it is even less common to switch from zebras to dangerous animals like buffaloes. For example, in other parts of Africa, larger lion colonies participate in buffalo hunting, but when zebras are more abundant, they still choose to hunt zebras. Their forced change of predation targets this time shows that the invasion of small ants has exerted great power and changed the fate of many large animals in the African savanna.
In the past, predators at the top of the food chain were often given more attention, believing that the disappearance of these species could have a significant impact on the local food chain and food web, for example by altering the population and behaviour of prey, and causing further changes. However, the new study sheds light on the important role played by organisms with lower trophic levels in the food chain: they do not necessarily affect species populations in a predator-prey relationship, and may also affect apex predators in a different way of non-trophic interaction.