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The bigger the gang, the more successful the lions are
Lions form prides to defend territory against other lions, not to improve their hunting success, a study reveals.
In doing so, they act much like street gangs, gathering together to protect their turf from interlopers, says a leading lion expert.
The bigger the gang, the more successful the lions are, information that could help conserve wild lions.
The discovery helps explain why lions, uniquely among the cat species, live together in social groups.
Lions stand out amongst all the cat species for their gregarious nature.
Across Africa and Asia, lions form prides of varying sizes comprising one or more males and often numerous females and cubs.
But why they do so has remained a mystery. A long-standing idea is that female lions socialise in order to hunt cooperatively. But despite the common sight of multiple females working together to outflank and bring down large prey, there is no clear link between how many lions hunt together and their hunting success.
Another is that lions gather to protect territory. Indeed, a range of animals from social insects to primates form social groups that defend territories against competitors.
But while there has been anecdotal evidence that bigger groups have a competitive advantage, the idea has never been rigorously tested over long periods of time.
That has now changed with a study analysing the behaviour of 46 lion prides living in the Serengeti National Park, Tanzania.
Conducted by ecologists Anna Mosser and Craig Packer of the University of Minnesota in St Paul, US, the study collated data about the prides' behaviour over 38 years, including where they ranged, their composition and how they interacted.
Mosser's and Packer's key finding was that competition between lion prides significantly affects the mortality and reproductive success of female lions, they report in the journal Animal Behaviour.
Male lions kill females to influence the balance of power
Larger prides with more adult females not only produced more cubs, as might be expected, but the females within these prides were less likely to be wounded or killed by other lions.
Prides with more females were also more likely to gain control of areas disputed with neighbouring prides, and those prides that recruited lone females improved the quality of their territory.
"The most important way to think about this is that lion prides are like street gangs," says Packer.
"They compete for turf. The bigger the gang, the more successful it is at controlling the best areas. The main difference from humans is that these are gangs of female lions."
Best 'real estate'
Both researchers think the study, alongside other work they have yet to publish, finally confirms that bigger prides form to defend territory.
"The advantage of large group size for group-territorial animals has been suspected for a long time, but had never been proven with data," says Mosser. "With this paper, we were able to do just that because of the many groups studied over a long period."
One surprise revealed by the research is that male lions turn out to play a much bigger role in how prides interact than expected.
LION FAMILY LIFE
A lion pride is made of one to 21 females, their offspring, and a temporary coalition of 1 to 9 males
One-third of female lions in the Serengeti leave their mother's pride to form a new one
Males leave their pride by age 4, to go solo or form a coalition with other males
Large coalitions of female lions are so successful at dominating small neighbouring prides that male lions step in to try to alter the balance of power. Males will often attack and attempt to kill female lions in neighbouring prides to tip the odds in favour of their own pride.
"Males turn out to be playing a greater role than we realised," says Packer. "Males attack females from neighbouring prides, likely altering the balance of power in favour of 'their' females."
The territorial advantages gained by coming together into larger social groups would have driven the evolution of social behaviour in lions, say the researchers.
"It also confirms a pattern that is probably applicable for many species, including group-territorial ants, birds, and chimpanzees," says Mosser, who is now at The Jane Goodhall Institute, in Kigoma, Tanzania.
Such insights will help with the conservation of lions, the numbers of which are suspected to have fallen by at least a third across Africa over the past two decades.
The research shows that "the lions are competing for relatively scarce 'hotspots' of high value real estate," says Packer.
So "lion numbers are ultimately limited by the number of hotspots that are safely inside national parks".