Giraffes 'winning by a neck'
Instead, du Toit is a researcher and professor. Head of the Department of Wildland Resources at Utah State University, Logan, his report still has as catchy a title as any Kipling could have come up with: "Winning by a Neck: Tall Giraffes Avoid Competing with Shorter Browsers."
The report, printed in this month's edition of "The American Naturalist," is co-authored by Elissa Z. Cameron of the University of Pretoria, South Africa. Du Toit himself is originally from Zimbabwe, did his post-doctoral research at USU in the 1980s, returned to Africa and was director of the Mammal Research Institution at the University of Pretoria, before coming back to Utah.
At USU he is not only a researcher and the chief of the Wildland Resources Department, but is also a teaching professor. He continues his work in South Africa, commuting occasionally to that country.
In a telephone interview, he gave an example that helps in understanding why the giraffe has such a gigantic reach. Each morning, du Toit eats a bowl of cereal. His robust breakfast contains oats, fiber, nuts, raisins and, he joked, "petrified fruit."
"My solution is, I stand up and I eat standing," so she can't reach the bowl.
As far back as 1871, scientists suggested that the giraffe evolved a long neck because of foraging competition with other animals, according to du Toit and Cameron. That was accepted for more than a century because it seemed obvious.
But in 1996, other scientists suggested that other reasons, such as giraffes attracting the opposite sex, could be the cause.
Until now, nobody had tested the idea that competition was the reason. But Cameron and du Toit set out to do that, putting up exclosures around certain acacia trees and not around others, in an experiment carried out in a South African private game preserve. The fences kept smaller browsers from reaching the lower leaves and branches, while giraffes could reach higher.
Three levels of browsing were sampled: above 4 meters (about 13 feet), available only to giraffes; 2.5 meters (about 8 feet), available to giraffes and kudus; and 1 meter (a little over 3 feet), material that could be eaten by steenboks, impalas, kudus and giraffes.
Measuring the amount of biomass eaten showed that, in words of the report, ordinarily "giraffe feeding efficiency is reduced at low heights" because of competition with smaller animals.
Relatively short herbivores have an advantage in selecting more desirable shoots, which grows lower. They have narrow muzzles, allowing them to pluck out the tastier treats from among the acacia's thorns.
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