Once the victorious males have taken over a pride, they kill all the existing cubsan act of infanticide that expedites a female lion's readiness to mate with one of the newcomers.
The new males stay around for several yearsusually up to four yearsto protect the group and its territory against other potential intruders. Eventually, however, a nomadic gang of males succeeds in overtaking the pride, and the cycle starts all over again.
"Life as a lion is pretty fast and furious," Packer noted.
In this tumultuous lifestyle, female lions equally share the burdens of childbearing and motherhood. This behavior, Packer and his colleagues say, is consistent with models of egalitarian theory.
Research into animal behavior has shown that egalitarianism is usually limited to species in which a single female is unable to control the reproductive habits of other females in the group.
That kind of control would be particularly difficult for lions to achieve, Packer explained, because the violent nature of their rivalry probably serves as a deterrent to despotic behavior. Potentially lethal claws and teeth pose a significant risk of what Packer calls mutually assured destructiona risk that's greater than in any other social species.
As a result, female colleagues in a pride don't harass one another or assert their dominance in social interactions, according to the researchers.
"On the one hand, they can be very aggressive to each other. They can be very dangerous companions to havethey are armed to the teeth, so to speak," said Packer. "On the other hand," he added, "there is some positive motivation to work together."
Female lions, like all feline species, slink off to give birth in secrecy. This keeps the young, vulnerable cubs away from potential female despots within the pride, and also hides them from nomadic males and predators such as hyenas.
Once a female lion has returned to the pride with her cubs, she raises them alongside other new mothers in a nursery group, or crèche. Only mothers with cubs of roughly the same age form a crèche. The advantage of this close association is that multiple mothers are available to defend the cubs against potentially infanticidal malesessentially, an instance of greater safety in numbers.
The researchers' data show that cubs are more likely to survive when they are raised in a nursery rather than by a solitary mother. This advantage of reproductive success gives female lions an incentive to synchronize their breeding, which they do.
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