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Elephants Don't Always Keep It in the Family
15 July 2009 (All day)
In elephant society, nothing is more important than family. From traveling packs of mothers and calves to larger groups that contain aunts and cousins, all segments of the creature's complex social structure are typically composed of relatives. But what happens when these populations are decimated by humans? New research reveals that elephants sometimes bring in non-kin to keep their social groups viable.
The finding is based on a survey of about 400 elephants living in Kenya's Samburu National Reserve. The elephants are part of a larger population that lost three-quarters of its members to ivory poachers in the 1970s. Today, the group remains vulnerable to illegal killing by nomadic tribes, farmers, and others.
Curious about how such devastation has affected the social structure of the Samburu elephants, conservation biologist George Wittemyer of Colorado State University in Fort Collins and colleagues studied the creatures for 5 years. They pinpointed the elephants' genetic relationships to each other by sequencing DNA from fresh dung samples. The researchers found that when they looked at the largest groupings of elephants in this society--so-called "clan" and "bond" groups--many of the elephants had opened up to include nonrelatives.
Wittemyer, whose team reports its findings today in the Proceedings of the Royal Society B, says the elephants may be willing to accept nonrelatives into their group to ensure they have the critical mass needed to gather food and protect themselves. "The results indicate that the illegal killing of elephants can erode the genetic basis for their social structure but does not necessarily destabilize their social organization." Co-author Iain Douglas-Hamilton, an Oxford University zoologist who also directs the Kenya-based Save the Elephants charity, says the research "helps us to understand the extent to which an elephant society is disrupted by ongoing mortality from poaching but can yet adapt and recover."
Still, wildlife biologist Kathleen Gobush, who studied elephant groups as part of the University of Washington's Center for Conservation Biology, says that mixing with nonrelatives can come with "real long-term costs." Gobush and colleagues found similar nonkinship elephant groups in a shorter-term study of elephants in Tanzania's Mikumi National Park, where poachers killed three-quarters of the elephants before the 1989 ban on the ivory trade. In a separate study about to be published, Gobush also found evidence that such mixing causes "significant behavioral differences" between elephant groups of kin in contrast to groups of non-kin. For example, she says, mixed groups showed aggressive behavior at water holes more often than groups composed solely of kin.
Other elephant experts say they are intrigued by the findings but would like to see similar studies in other populations. Ecologist Caitlin O'Connell-Rodwell of Stanford University in Palo Alto, California, studies elephants in Namibia and says that "it would be great to get this kind of data from other disturbed populations to see if the pattern is consistent or just a local phenomenon that could have other explanations."