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9/28/2015 Cracking the Code of Predator-Prey Relations One Lion at a Time | THE WILDLIFE SOCIETY
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Cracking the Code of Predator-PreyRelations One Lion at a TimeBy Joshua Rapp Learn
Posted on September 17, 2015
Lions attack a buffalo.Image Credit: Amoury Laporte
A huge, healthy population of prey may be too much for predators to feast their eyes on — atleast proportionately.
Researchers have discovered a widely applicable principle that could explain the maximumcarrying capacity of predators that a given prey base could support.
“What we now have is a baseline for how many predators there should be, given a certainamount of prey,” said Ian Hatton, who was a PhD student at McGill University while working ona study recently published in Science. “All these different ecosystems lined up along thispattern.”
Hatton began by studying large mammals across protected areas of Africa. He comparedpublished studies on the number of lions and other predators in the Kalahari Desert, whichdoesn’t have much prey to go around, with those of the Ngorongoro Crater — a lush areapacked with wildebeest and other prey.
“We gathered as much data as we could,” Hatton said, adding that a lot has been publishedsince the 1950s.
He and the other researchers found a “very striking” pattern: The number of predators didn’tincrease proportionately with the number of prey.
In the Ngorongoro Crater, which Hatton said has one of the highest densities of prey on theplanet, “there are three times less predators for every pound of prey,” he said.
But the declining ratio of predators seemed to match closely with another statistic.
As populations of most animals increase in a given area, things become crowded, and the
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9/28/2015 Cracking the Code of Predator-Prey Relations One Lion at a Time | THE WILDLIFE SOCIETY
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A lion feeds on a buffalo. Image Credit:Amoury Laporte
Africa Alaska Food chain Lions prey-predator relations Quebec Wolves
proportion of overall reproduction begins to drop. For a lion this means that there are moreable-bodied adult wildebeests and less calves, which generally make for a comparatively easymeal.
“The constant stream of new food supporting the predator population decreases,” Hatton said.They had found their match.
From Africa to the World
The study didn’t stop with African mammals.Researchers gathered data from approximately 1,000different predator-prey studies from ecosystems allover the world, including tigers in Southeast Asia,wolves and their prey from Alaska to Quebec, and evenzooplankton eating algae in oceans and lakes.
“We also looked at production and biomass,” Hattonsaid. “Basically everywhere we looked we found thissame pattern, this same mathematical function todescribe this system.”
Carolyn Kurle, an assistant biology professor at theUniversity of California-San Diego who has studiedother predator-prey relations, said that this study puts a new twist on an old debate amongecologists about whether the natural world is governed through food webs from the top-downor bottom-up.
“With top-down regulation, predators keep their prey numbers low, which releases plants fromexcess herbivory which allows the world to be green,” Kurle said. Bottom-up regulation, on theother hand, says that “when systems are less productive, all levels of the food web above arekept in check.”
But this study shows that the control comes from the bottom up, but it is not linked to primaryproduction as researchers usually assumed. “Highly productive regions support more prey, butthe crowding lowers prey reproduction, which in turn helps keep predators in check.
She said the results of this study also show how useful long-term census data can be to largestudies like this.
Joshua Rapp Learn is a science writer at The Wildlife Society. Contact himat [email protected] with tips or story suggestions on conservation,wildlife science, management or other story ideas. @JoshuaLearn1Read more of Joshua's articles.
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