In the past, only one of the four ant species was recognized as a cooperator, because it successfully defended the tree from elephants and other herbivores in exchange for using the tree's resources, Palmer said. The other three ants were thought to exhibit varying degrees of cheating behavior, he said.
The key to the new findings is the timing. When a species lives a long time, its needs may change drastically as it grows from young to old, and sequential associations with several partners may help it meet those needs at different times, he said.
"A human analogy might be that what we look for in romantic partnerships when we're younger perhaps a daring and exciting person who likes to be bold and take risks is not necessarily the thing that we are looking for in a romantic partner when we get older, when stability, the ability to hold down a job and provide for children becomes more important," he said. "The best possible partner is really a function of where you are in your life and what your needs are at that particular moment."
In the same way, a mutualistic species may require a partner that helps it survive during its vulnerable younger years, even if that partner prevents it from reproducing, Palmer said. Later in life, when large size makes individuals less vulnerable, the ideal partner may be one that enhances reproduction even as it reduces the chances of longer-term survival, he said.
Over eight years, Palmer and colleagues monitored annual survival, growth, reproduction and ant occupancy of 1,750 Acacia drepanolobium trees and constructed demographic models that related the trees' lifetime fitness to oc
|Contact: Todd Palmer|
University of Florida