Elissa Z. Cameron (University of Pretoria) and Johan T. du Toit (University of Pretoria and Utah State University), "Winning by a neck: tall giraffes avoid competing with shorter browsers"
Giraffes are well known for their unusual height, and they generally feed high in the tree canopy, above the height that other herbivores can reach. Text-books use the giraffe's elongated neck as an example of evolution by natural selection caused by competition between different species for the same leaves. Research by Elissa Cameron and Johan du Toit at the Mammal Research Institute in the Department of Zoology and Entomology at the University of Pretoria tested whether foraging competition could explain why giraffes feed mostly on leaves high in trees despite being able to feed at lower levels as well. Giraffes receive more leaves per bite by foraging high in the tree, which could be because small browsers eat some of the leaves at lower heights, or because more leaves grow at higher levels. Fences were built around trees in the greater Kruger National Park ecosystem to stop these smaller browsers from eating the leaves. After a complete growing season there was the same amount of leaves throughout the fenced trees, demonstrating that leaves were depleted by small browsers. Therefore, competition appears to drive the giraffes to forage high in the trees. "This provides the first real experimental evidence that the long neck of the giraffe might have evolved as a consequence of competition," states Elissa Cameron, "which provides support for the previously untested text-book example of natural selection."
Giraffes are the tallest mammals on Earth, with some males standing 19 feet high. Fossils show they evolved from a deer-like ancestor with a shorter neck.
That has got to be one of the lamest and dummess assed ezperiment Ive ever read about. Selectively fence out smaller browsers and then claim that your experiment was a success. Thats total sludge. They should canopy fence the tree tops also..
ABSTRACT: With their vertically elongated body form, giraffes generally feed above the level of other browsers within the savanna browsing guild, despite having access to foliage at lower levels. They ingest more leaf mass per bite when foraging high in the tree, perhaps because smaller, more selective browsers deplete shoots at lower levels or because trees differentially allocate resources to promote shoot growth in the upper canopy. We erected exclosures around individual Acacia nigrescens trees in the greater Kruger ecosystem, South Africa. After a complete growing season, we found no differences in leaf biomass per shoot across height zones in excluded trees but significant differences in control trees. We conclude that giraffes preferentially browse at high levels in the canopy to avoid competition with smaller browsers. Our findings are analogous with those from studies of grazing guilds and demonstrate that resource partitioning can be driven by competition when smaller foragers displace larger foragers from shared resources. This provides the first experimental support for the classic evolutionary hypothesis that vertical elongation of the giraffe body is an outcome of competition within the browsing ungulate guild.