CENTRAL AMERICAN CO-OP: In a three-member example of symbiosis, Campylorhynchus rufinucha, or rufous-naped wrens, live in acacia trees in Central America that are also home to aggressive ants. The trees provide food for the ants, the ants attack herbivores and would-be predators of the wren chicks, and the wrens protect the ants from other, ant-eating birds... Sharon Beals