Big Herbivores Shape the Land

Removing large herbivorous mammals from the African savanna can cause a dramatic shift in the relative abundance of species throughout the food chain, a new study suggests.

Researchers used large electric fences to exclude cattle, elephants, zebras and other herbivorous mammals from experimental plots on a ranch in central Kenya from May 2004 to December 2005. During that time, the scientists monitored changes in the populations of trees, beetles, lizards and other plant and animal species.

"All of the species studied increased in abundance in the absence of large plant-eating mammals," said lead study author Robert Pringle, a graduate student at Stanford University. These results are examples of what ecologists call cascading effects, he said.

Although elephants and zebras do not interact directly with insects, they share plants as a food source. Previous studies have shown that when elephants and zebras are experimentally removed or hunted out, plant matter accumulates and insect populations increase.

"With an increase in insects comes an increase in the insects' predators, such as lizards," Pringle said. "Thus, the actions of a few dominant species ripple throughout the ecosystem."

The study, published in the Jan. 2 edition of Proceedings of the National Academy of Sciences, is timely for several reasons. "Large herbivorous mammals are declining throughout Africa and worldwide, and have already gone extinct in many places," Pringle said. "Our results suggest that these declines are likely to have complicated, and often unanticipated, consequences for the entire ecosystem."

---LiveScience Staff

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Credit: Mark Shwartz, Stanford University