Dolphins Make Excellent Networkers!

By Danny Kingsley, ABC Science Online

July 17, 2003 — People who develop complex networks, like the World Wide Web or electricity grids, could learn a lot from the social behavior of dolphins, a New Zealand zoologist has found.

David Lusseau, a zoologist at the University of Otago, spent seven years observing a community of 64 bottlenose dolphins in Doubtful Sound, New Zealand, and found they have a social structure similar to human and human-made networks.

His mathematical study of their social behavior is published in the latest issue of the journal Proceedings of the Royal Society.

Many complex networks, including human societies, have properties that allow information to be exchanged quickly among members. Lusseau's study shows that animal societies are also organized in a manner that permits a quick and efficient transfer of information. Gregarious long-lived animals, such as gorillas, deer, elephants and bottlenose dolphins rely on information transfer to use their habitat.

Lusseau studied dolphin individuals that were seen together more often than expected by chance encounters. He identified the individuals from markings on their dorsal fins. And he found that the dolphin's social network is characterized by the presence of 'centers' of associations, with these hubs mainly being adult females.

It is possible to measure how information flows through a system by looking at hubs of information, and by counting the number of elements it needs to pass through to get from a designated starting point to a designated end point. Lusseau used this measurement, called "diameter."

"The global human population seems to have a diameter of six, meaning that any two humans can be linked using five intermediate acquaintances," he wrote. This is what is commonly referred to as "six degrees of separation."

Complex networks like electricity grids and the Web are more loosely organized, so it takes more steps to get somewhere. This opens them up to problems if some of the hubs are taken out.

Previous studies have found that the diameter of two large networks, the Internet and the Web, more than doubled when 2 percent of the nodes with the most links were removed. That means it would take twice as long to get from one element to another.

By comparison, the dolphin community showed great resilience to having hubs removed. The cohesiveness of the dolphin community remained unaffected by the removal of key individuals. The resilience properties of this network allow the maintenance of a cohesive society even if there was a catastrophe resulting in the loss of more than a third of the population.

"The ability for two individuals to be in contact is unaffected by the random removal of individuals," Lusseau said. "The removal of individuals with many links to others does affect the length of the 'information' path between two individuals, but it does not fragment the cohesion of the social network."

These self-organizing phenomena allow the network to remain united, even in the case of catastrophic death events. This property could be applied to human-made networks, such as the World Wide Web, which are seriously damaged by attacks that remove key nodes, argued Lusseau.

"This is one of the smallest networks of any type in which scale-free emerging properties have been observed. It provides further evidence that these self-organizing phenomena do not depend solely on the characteristics of individual systems, but are general laws of evolving networks," concluded Lusseau.

Source:  http://dsc.discovery.com/news/afp/20030714/dolphin.html