Scientists previously assumed that interaction networks without central control, known as self-directed networks, have universal properties that make them efficient at spreading information. Just think of the local grapevine: Let something slip, and it seems like no time at all before nearly everyone knows.
By observing interactions in ant colonies, University of Arizona researcher Anna Dornhaus and doctoral candidate Benjamin Blonder have uncovered new evidence that challenges the assumption that all interaction networks have the same properties that maximize their efficiency. The National Science Foundation-funded study was published in the Public Library of Science on May 20.
"Many people who have studied interaction networks in the past have found them to be very efficient at transferring resources," said Blonder. "The dominant paradigm has been that most self-organized networks tend to have this universal structure and that one should look for this structure and make predictions based on this structure. Our study challenges that and demonstrates that there are some interaction networks that don't have these properties yet are still clearly functional."
"There are a huge number of systems that are composed of interacting parts, and we really don't have a good sense of how these systems are organized," said Blonder. "Think of a city with many people or the Internet with many computers. You have all these parts doing their own thing and somehow achieving some greater function."
The researchers chose to use ant colonies as models for self-directed networks because they are composed of many individual components -- the ants -- with no apparent central organization and yet are able to function as a colony.
"We think no individual ant has a sense of purpose," said Blonder. "It doesn't go out one day and say: 'I'm going to move this pebble for the greater good of the society.' It has a behavioral program where if it sees a pebble, then it's likely to move it. The reason that contributes to the good of the colony is an evolutionary argument where the ants' behavior is shaped over thousands or millions of generations."
Dornhaus and Blonder studied colonies of Temnothorax rugatulus, an ant species that is common in southern Arizona.
"These ants like to live in little rock crevices such as underneath a rock or in a split in the rock," said Blonder. "The trick is convincing them to go from their nice little home on Mount Lemmon to the lab."
Which raises an interesting question: How does one collect an ant colony?
"It isn't easy," said Blonder. "You get an aspirator, which is a tube with a fine mesh on the end of it so you don't inhale the ants, and you put the tube down in the colony and you suck. And the ants come up and you blow them out into a container to transport them to the lab."
"Of course, once you flip the rock over, the ants are upset. You have to get them before they all run off somewhere. And you also have to get the queen because without the queen the colony will die."
The queen, the mother ultimatum among ants, is the only member of the colony that reproduces. Without her, there would be no new ant workers and the colony would die.
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