We could hear the elephants coming toward us before we could see them: The sound of limbs snapping and trees toppling made it obvious that an elephant deforestation project was underway. Soon they emerged into a clearing, chomping on branches.
Elephants are not dainty herbivores, so there are large portions of African savanna that have become relatively treeless. On the other hand, satellite images of Kenya taken over several recent years showed that there were areas where tree coverage has remained stable. That was in spite of increases in elephant population in those same areas, which raised the reasonable question “Why?”
A study published last month in Current Biology came up with an answer. It turns out that ants are defending the trees from elephants. Yes — ants. It would seem like a mismatch, since your average ant weighs abut 5 milligrams dripping wet, and your average African elephant weighs 250 pounds — at birth — and several tons when fully grown.
Biologists Todd Palmer of the University of Florida and Jacob Goheen of University of Wyoming conducted a study to investigate the connection between ants and stands of acacia trees that elephants wouldn’t eat. In one experiment, they removed ants from acacia trees to see if there was something in the tree’s chemistry that repulsed the pachyderms. Not at all — the elephants gobbled up those branches.
In the second experiment, the scientists added ants to other species of trees that are frequently on the elephants’ menu. The assumption was that if the ants were in fact a deterrent, the elephants would shun these ant-adulterated morsels. “Sure enough,” Goheen said, “the elephants were choosing to eat more or less entirely based on whether or not these trees were defended by ants.”
It seems that the ants drive off the elephants by crawling into the elephants’ nostrils and biting them. Elephants don’t like ants up their trunks, just as human beachgoers don’t like sand up their trunks. By the way, ants don’t deter giraffes, because they are able to swipe the ants away with their long tongues.
Anyway, this arrangement between acacia trees and ants is what scientists call SYMBIOSIS. You may recall from your high school biology class that symbiosis is cooperation between two species to their mutual benefit. Thanks to the ants scaring away the elephants, the trees get to live. And what do the ants get out of the deal? They get rent-free lodging and food — they eat the sap that the tree excretes.
Meanwhile, the elephants go elsewhere to find ant-free trees. Those are typically in areas that have sandy soil; the ants seem to prefer acacia trees that grow in soil that is primarily clay.
Since human beings benefit from having plentiful trees on our planet (they filter out bad stuff and generate oxygen), those ants in Africa are indirectly helping us, too. It’s strange to think that ants have our back, isn’t it? Oh wait, there’s one on your shoulder now. I’ll get it, hold still…