Feb. 21, 2008 -- The squirrel world has its own Kevin Bacon -- a socially well-connected individual dubbed Mercedes by the scientist who studies him.
The major difference between human and squirrel social networks is that people, as the conventional wisdom goes, appear to be "separated" by five or six degrees. For squirrels, it takes only three connections for one member of a population to get to any other.
"It's the same thing," said Theodore Manno, a biologist at Auburn University in Alabama. "Squirrels with many connections tend to befriend squirrels that are like them; squirrels without many connections tend to befriend squirrels like them as well."
"Isn't that the same as the popular crowd going to each other's Facebooks and the skater kids doing the same?" he asked.
The discovery that squirrels have social networks not only illustrates the complexities of animal behavior, but also says something about the properties shared by all networks.
Manno pursued the idea after F. Stephen Dobson, also at Auburn University, suggested that network theory could be applied to social interactions within a squirrel colony.
Manno observed 65 wild, free-ranging Columbian ground squirrels in Sheep River Provincial Park in Alberta, Canada. After naming and taking notes on each squirrel, Manno watched and recorded details about their social behaviors -- including "kissing" (oral contact that doesn't lead to bickering), sniffing, playing and grooming.
Over the course of the study, which will be published in the April issue of Animal Behavior, Manno observed 2,200 such interactions. Using a software tool called UCINET that has identified networks among airplane hubs, bridge supports, the Internet, human and animal societies and more, he charted connections between the squirrels.
Mercedes, for example, was linked to the squirrels 7-Up, 3-Cherry, Eighth Notes and Princess Pea.
Most of the connections were between mating squirrels and their families. But friendship, too, exists in the squirrel world, said Manno. He even has a way to measure it.
"Squirrels have preferred companionships," he explained. "If they interact amicably more than they would just by meeting each other in the general course of things -- calculated through a complicated mathematical formula -- then they are 'friends.'"
Using the software, Manno tested what would happen to the squirrel network if individuals were removed. Random removals didn't disrupt the network much, but if more than 10 percent of the colony's important members were taken out, the network fragmented, leaving it vulnerable to collapse.
"Importance" in a squirrel colony generally refers to "adult males that are putting out feelers for sex opportunities (like Mercedes) or...adult females that are experienced at mating and want to have their choice of a bunch of males," he said.
Manno said populations of other social animals -- primates, fish, killer whales, dolphins -- could experience comparable collapses when disrupted.
Conversely, if the wildlife management resources are available, special attention to important animal networkers could strengthen animal groups, Manno theorizes.
"What I like about this paper is that it shows individuals have different relationships with others," said Daniel Blumstein, an associate professor of ecology and evolutionary biology at the University of California at Los Angeles, studies marmot social networks with colleague Tina Wey.
"While not novel, using formal social network analyses to quantify it in a free-living, non-human animal system is a relatively recent application of these statistical tools," he said.
Diseases might be better controlled in animal societies if key networkers, which might become "super-spreaders," are removed, perhaps temporarily, added Blumstein.
Wey hopes future research will also address the biological significance of social networks.
"For example," she said, "what does it mean to a ground squirrel to interact with others in the context of a network? How is this manifested in terms of biological fitness?"
"These are questions we have also struggled with, and I think there is a lot more to be done before we can answer them more comprehensively."
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