Brief piece in Science section of today's NY Times. Abstracts recent article in Nature reporting research ou of UC Davis. A particular species of ant - one of several - which inhabits galls on a form of acacia tre in Africa routinely prunes branches which get too close to other trees so as to avoid invasion by ant colonies of more aggressive species in neighboring trees. They do not bother to prune sides not facing other trees.
So, can you see the tribesmen sitting under the Acacia? "Gee I wonder what causes Summer Limb Drop on these Acacia trees, doesn't seem to happen to the baobab trees."