Africa's Biggest Mammals Key to Ant-plant Teamwork
Posted by sky | Tags: Animals, Science, cooperation, insect, interdependence, nature, plant, relationships
From ScienceDaily.Throughout the tropics, ants and Acacia trees live together in intricate interdependent relationships that have long fascinated scientists. Now researchers are reporting that in Africa, this plant-insect teamwork depends on the very antagonist it is intended to ward off: Africa's big browsing mammals. Researchers report that elephants, giraffes and other large plant-eaters spur Acacias to "hire" and support ants as bodyguards -- and without the mammals, the trees slash their investment in ants, opening both to other attackers. Acacias are mostly shrubby trees common across the tropics and sub-Saharan African savannah. They have swollen thorns that serve as nests for three species of biting ants. Healthy trees have hundreds of the thorns, often containing more than 100,000 ants per tree. Both the ants and the trees benefit from their close cohabitation. The ants get the thorny shelters, as well as nectar they collect from the bases of Acacia leaves. Because the ants swarm in defense against anything that molests the trees, the trees get protection from their chief ostensible nemeses, browsing animals. That's when the mutualism is working well. But the research got its start when Palmer noticed that certain Acacias at his research site in central Kenya, which had been fenced off from wild herbivores, looked sickly compared with their unfenced counterparts. That was the opposite of what might be expected, because the browsers feed voraciously on the trees. Without mammals around to eat the trees, sheltering fewer, less aggressive ants would not present a cost to the trees. But the research revealed that the fewer colonies of weakened ants become less able to defend their territory from another species of ant that, unlike the others, does not have a mutually beneficial relationship with Acacias. Instead, this fourth ant species feeds away from the tree and does not protect it from attackers -- in fact, it actually encourages a destructive, wood-boring beetle whose cavities then serve as this ant's home. The result appears to be that the trees untouched by browsing mammals are infested with more of the beetles, which is part of the reason that they fare poorly. One irony of the findings is that the trees have developed their mutualistic relationship with the ants to protect themselves against plant-eating mammals -- and yet because of that relationship, the trees wind up actually needing the mammals. "If you get rid of the large mammals, it shifts the balance of power, because the trees default on their end of the bargain," Palmer said. "When the trees opt out, their hard-working employees starve and grow weak, which causes them to lose out. So, ironically, getting rid of the mammals causes individual trees to grow more slowly and die younger." The research has important implications for conservation.Previous Post Next Post