Einstein Science Reporting for Kids
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21-Jan-2005

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Lion lifestyle logic



A lioness approaches her prey. Image Science.

In the story of The Lion King, lion cub Simba learns about how everything lives together in a delicate balance called "the circle of life." It's no wonder Simba needed a song to make sense of it all: up close, Africa's Serengeti lions and the animals and plants they depend on interact in a way that looks more like a big messy tangle than a circle.

One of the most puzzling things about lion lifestyles is that lion populations in the Serengeti stay pretty much the same size for years and then suddenly get larger or smaller. Understanding what causes lion populations to grow and shrink should be important for protecting the lions, since these animals are also threatened by human activities.

In a study in the 21 January 2005 issue of the journal Science, Craig Packer of the University of Minnesota and his colleagues investigated why those jumps seem to occur out of the blue.

The scientists looked at records from the last several decades that kept track of the numbers of lions, the numbers of their prey (such as wildebeests, gazelles and zebras), and the amount of grass available for these prey animals to graze on.

Surprisingly, the amounts of prey and plants changed gradually, unlike the lion numbers.

The researchers determined that an important piece of the puzzle was the way that groups of lions, called "prides," split when they reach a certain size. Because the males defend territory while the females do the hunting, prides must have just the right ratio of males to females in order to make sure that there is enough food and that the lion dens are protected.

Typically, a small group of related females will leave a pride and set off to start their own, and then they'll be joined be a smaller number of males. Baby cubs can only be born and grow up to be adults when their prides have just the right amount of food, territory and male lions.

The scientists determined that sometimes all these different pieces fit together just right, allowing lots of cubs to be born and the lion population sizes to shoot up. And, sometimes, the pieces don't work together at all, and the population size drops.

Thus, the sudden jumps in lion numbers that Packer's team had found so puzzling didn't actually happen out of the blue. The changes just involved so many pieces that the researcher needed to study a long period of time in order to see the whole picture.

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