Unpredictable Consequences
"If you had asked me 10 years ago 'what would happen if you took large mammals out of the system,' I would have answered 'I'll bet the trees would be really happy!'" he said.
Instead, because the browsing animals are the driving force behind the tree paying out benefits to the ants, when the payments diminish, the ants that protect the tree begin to starve and its colonies become smaller.
Some ants reduced their defensive behavior and began tending colonies of insects that bore into the plants and extract sugars.
"So, that's one lesson from the research, to me: The human-induced decline of big herbivores in Africa can have some pretty dramatic and non-intuitive consequences for the communities in which these large mammals live," Palmer said.
Ted R. Schultz, a research entomologist at the Smithsonian Institution's National Museum of Natural History, said the harm the plant caused by the removal of large animals "is surprising, and it's not the kind of thing anybody would have been likely to predict in advance."
Schultz, who was not part of Palmer's research team, said the report shows that mutualisms are finely balanced and complex.
"The system reported here is a balance of a number of players—the trees, the browsing mammals, the main ant, and three other ant species, with the ants all competing for the trees. Remove one of the players—the browsing mammals—and all the other moving parts rearrange themselves in a way we hardly could have predicted." he said.
Snapping Back?
So, can the trees recover their protective ants if large animals start nibbling on then again?
Palmer intends to find out by exposing the trees again to browsing, "to see how quickly trees will re-induce their investments in symbiotic ants, and in turn, whether such reinvestment will be enough and in time, or too little, too late."
The research was funded by the U.S. National Science Foundation, the Smithsonian Institution, National Geographic Society, and the African Elephant Program of the U.S. Fish and Wildlife Service.
National Geographic Society owns National Geographic News.
Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
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