Associated Press
Call it the rule of unintended consequences—drop your guard because one threat goes away and an unexpected menace jumps up and smacks you. Or that's how it goes for African acacia trees, new research suggests.
It's a lesson in environmental complexity.
For thousands of years these thorny shrubs have provided food and shelter to aggressive biting ants, which protect the trees by attacking animals that try to eat the acacia leaves.
Called mutualism, this arrangement has been a good deal for both the trees and the ants.
Scientists studying the decline in large animals in Africa wondered what would happen if the creatures no longer were eating the leaves. They fenced off some of the acacias, so elephants, giraffes, and other animals couldn't get to them.
Revenge for Neglect
Surprisingly, after a few years, the fenced-in trees looked sickly and grew slower than their unfenced relatives.
Without animals eating their leaves, the trees no longer bothered to take care of the ants—they reduced nectar production and made fewer swollen thorns for the ants to live in.
The result: The protective ants either began damaging the plant or were replaced by other insects that ate holes in the bark.
"Although this mutualism between ants and plants has likely evolved over very long timescales, it falls apart very, very rapidly," said Todd Palmer, an assistant professor of zoology at the University of Florida.
"Over the course of only ten years, we found that when mammals could not eat plants, the plants began to have less use for the ants, and therefore began to reduce their 'payments' to the ants, in the form of nectar," Palmer, who is currently in Kenya, explained in an email interview.
Palmer's findings are reported in Friday's edition of the journal Science.
