A few well-connected dolphins keep pods together

Without these individuals, the cohesion of the dolphin group falls apart, researchers have discovered.

The finding may mean that capturing wild dolphins or killer whales for marine parks could have a serious impact on their companions left behind.

Details of the study, by a UK and US research team, are outlined in New Scientist magazine.

Ecologist David Lusseau, from the University of Aberdeen, UK, studied the social interctions of a community of 62 bottlenose dolphins living in Doubtful Sound, New Zealand.

Chance encounters?

From 1994 to 2001, he tracked individual animals and worked out which ones appeared together more often than would be expected by chance.

His colleague, Mark Newman from the University of Michigan in Ann Arbor, US, then applied a mathematical technique used for probing complex networks.

What emerged were two sizeable sub-communities joined together tenuously by just a few common members.

These dolphins occupied central roles in the social network. But without them, the entire network was likely to split into two.

"Remarkably this is exactly what happened," Newman told New Scientist magazine. "Some years into the study, two of these keystone individuals did indeed disappear, and the community split into two separate groups that went their own way."

When the missing individuals returned, the pod re-formed.

The results of the study are to be published in a future issue of the Royal Society journal Biology Letters.