Grazing on the savanna: Wide dietary preferences revealed

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This graphic depicts the diet composition and overlap of the target species. Lines connect the species (outer boxes) to dietary plant sequences (inner boxes), which are colored by plant family. Widths of inner boxes are scaled to reflect how frequently each sequence was detected across all samples from all LMH species; line widths show how frequently each plant was detected in samples from each species. Plants detected in both grazer and nongrazer diets appear in both networks. Boxes are ordered to minimize overlapping lines.
This graphic depicts the diet composition and overlap of the target species. Lines connect the species (outer boxes) to dietary plant sequences (inner boxes), which are colored by plant family. Widths of inner boxes are scaled to reflect how frequently each sequence was detected across all samples from all LMH species; line widths show how frequently each plant was detected in samples from each species. Plants detected in both grazer and nongrazer diets appear in both networks. Boxes are ordered to minimize overlapping lines.

Researchers have gained the clearest picture yet of the grazing habits of animals on the semi-arid African plains, revealing wide dietary preferences.

The American researchers from Princeton University and the Smithsonian Institution concentrated on seven species – the Plains zebra, Grevy’s zebra, elephants, impalas, Cape buffalo, the dik-dik antelope and domesticated cattle. These represented 99 percent of the herbivores in the study location.

They traveled to Kenya’s Mpala Research Center and Conservancy, where they collected 300 fresh dung samples for analysis using a technique called DNA metabarcoding. The technique allowed them to identify the different plant species each animal was eating.

Tyler Kartzinel and her colleagues found significant dietary variations, even between the Plains and Grevy’s zebras.

It was found that the zebra species ate about 45 species of plants, but 15 species differed significantly between their diets — 10 on the Grevy zebra’s list of favorites, and five on the plains zebra’s. This represented a third of the food types in either zebra species’ diet.

They found that diet composition was similar within species, but strongly divergent across species.

The findings supported the theory that large mammalian herbivores partitioned food resources in order to coexist, and provided valuable insights into how this occurred.

The research team said the finely tuned diets suggested diversity in large plant-eating mammals may be more tightly linked to plant diversity than was currently recognized.

zebra-lewis_0178“Dietary overlap was greatest between species that were similar in body size and proportional grass consumption,” the researchers reported in the Proceedings of the National Academy of Sciences.

“Nonetheless, diet composition differed between all species — even pairs of grazers matched in size, digestive physiology, and location — and dietary similarity was sometimes greater across grazing and browsing guilds than within them.”

The researchers said their data was gathered during a wet season when food was abundant. “Available evidence suggests that our results are therefore likely to conservatively describe dietary separation.”

They noted that overlap and competition between wildlife and livestock in rangelands remained a major source of human-wildlife conflict around the globe. However, the extent of dietary overlap was poorly understood due to difficulties in studying wildlife diets.

Controlled studies using the same DNA metabarcoding technique could help inform management strategies, they said.

Tyler R. Kartzinel, Patricia A. Chen, Tyler C. Coverdale, David L. Erickson, W. John Kress, Maria L. Kuzmina, Daniel I. Rubenstein, Wei Wang, and Robert M. Pringle
DNA metabarcoding illuminates dietary niche partitioning by African large herbivores
PNAS 2015 ; published ahead of print June 1, 2015, doi:10.1073/pnas.1503283112
The full study can read here.

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